Any time previously unreleased Prince music sees the light of day, it's a cause for celebration. But the release of the super deluxe edition of Sign O' the Times nearly warrants a parade.

Put simply, there's never been a box set covering the scope of his music in such detail: the new set features the newly-remastered 1987 double album; 13 B-sides, remixes and edits; two unreleased concerts (an audio-only showcase from Utrecht, The Netherlands and a filmed set at Paisley Park on New Year's Eve 1987), and - across three CDs or six LPs - a whopping 45 previously unreleased outtakes from the vault that paint even more details on the making of this classic album and several unrealized projects assembled between 1985 and 1986.

Ahead of the set's release on Friday, Sept. 25, we've combed through our bootlegs and put together a guide to the vault selections, from alternate versions of hits and long-coveted outtakes to a few things even the truest funk soldier might not know about.

"I Could Never Take the Place of Your Man" (1979 Version)

The oldest track from the Sign O' the Times box is a version of the album's third Top 10 smash recorded more than a decade earlier, during the sessions for Prince's second album. It was one of a half-dozen tracks released in the months leading up to the set's release.

"Teacher, Teacher" (1985 Version)

Another track that predates the Sign O' the Times era, "Teacher, Teacher" was first conceived in 1982 (an early version was issued on the super deluxe edition of 1999 last year) and updated by the Revolution's Wendy Melvoin and Lisa Coleman for the unrealized Prince and the Revolution album Dream Factory.

"All My Dreams"

Long before "Adore," "All My Dreams" was the intended closer to Dream Factory as it expanded from one LP in the spring of 1986 to two later that summer.

"Can I Play with U?" (feat. Miles Davis)

One of two appearances of the jazz legend on the Sign O' the Times box (he also cameos during the live set at Paisley Park included on the set's DVD), "Can I Play with U?" came close to a release nearly 20 years ago, on a box set of Miles Davis' Warner-era material.

"Wonderful Day" (Original Version)

Though "Wonderful Day" was soon discarded from later intended configurations of Dream Factory, it's a track sharp-eared fans have heard before, underscoring a scene in Prince's 1986 film Under the Cherry Moon.

"Strange Relationship" (Original Version)

Dream Factory was to feature more collaboration between Prince and Wendy & Lisa than any prior release. This alternate "Strange Relationship" was massaged into the original album version after Prince disbanded the Revolution.

"Visions"

This striking piano piece by Coleman was earmarked to open the never-released Dream Factory; Wendy & Lisa later resurrected it for a bonus disc of piano improvisations included with some copies of their 1990 album Eroica.

"The Ballad of Dorothy Parker" (with Horns)

This favorite album cut from Sign O' the Times - the first to be recorded in the studio at his Galpin Blvd. home in Chanhassen, Minnesota - originally featured a complex brass chart that was mixed out of the final release.

"Witness 4 The Prosecution" (Version 1)

The very first track from the deluxe Sign O' the Times unveiled ahead of the box set's release was a peppy collaboration with Wendy & Lisa, originally earmarked for Dream Factory but later completely re-recorded after the Revolution broke up.

"Power Fantastic" (Live in Studio)

A shorter version of this jazzy cut intended for Dream Factory was released in 1993, part of the compilation box set The Hits/The B-Sides.

"And That Says What?"

This instrumental jam, so named for the phrase Prince yelled during the take, was also intended for early versions of Dream Factory.

"Love and Sex" (1986 Version)

Prince and drummer Sheila E. put this track together with intentions to use it for her third album; two years earlier, the title was used for an outtake released in 2017 on the deluxe edition of Purple Rain.

"A Place in Heaven" (Prince Vocal)

This piano-led ballad was sung by Coleman for inclusion on Dream Factory, but Prince was prone to offering guide vocals to his tracks. That's the version heard here.

"Colors"

Another abandoned Dream Factory track, this short guitar instrumental by Melvoin was slated to precede "I Could Never Take the Place of Your Man" on that album's running order.

"Crystal Ball" (7" Mix)

This sprawling, introspective track was earmarked for both Dream Factory and triple-album follow-up Crystal Ball, which was cut down to two albums and released as Sign O' the Times. But the existence of a short single version is one of many surprises on the deluxe set.

"Big Tall Wall" (Version 1)

A surprisingly upbeat track, given its subject matter. The tune refers to Prince's reaction when then-girlfriend Susannah Melvoin (sister of Wendy) got an apartment of her own. "Big Tall Wall" was another early contender for Dream Factory that was shed as the album got longer.

"Nevaeh Ni Ecalp A"

A back-masked segment of Lisa singing "A Place in Heaven" was intended for various configurations of Dream Factory when it expanded from one album to two.

"In a Large Room with No Light"

While "In a Large Room with No Light" was another casualty of Dream Factory's expanding track list, it was one of a few songs from the era Prince would revisit much later on. A new version was streamed in 2009 to commemorate his headlining sets at the Montreux Jazz Festival that year.

"Train"

One last track intended for the Dream Factory album, "Train" features a chugging rhythm and lyrics alluding to the separation of lovers - perhaps a hint to the Revolution's impending demise.

"It Ain't Over 'Til the Fat Lady Sings"

One of the least-known songs from Prince's prolific 1986, it may have been earmarked for a different Dream Factory project intended for the stage, but fully scrapped by year's end.

"Eggplant" (Original Prince Vocal)

A treasured, uncommon rarity among Prince collectors, bootlegged versions of "Eggplant" usually feature vocals by Wendy, not the artist himself.

"Everybody Want What They Don't Got"

Precious little is known about this 1986 outtake, but that almost wasn't the case several decades ago. Fans at the 2000 Celebration at Paisley Park could vote on potential tracks for a follow-up to 1998's outtakes collection Crystal Ball - and this song was one of the finalists. (Lyrics to the track also appeared in the book Neo Manifesto, alongside photos from the Act II Tour in 1993.)

"Blanche"

According to legend, this jam was recorded the same day as a much bigger tune in Prince's canon: the title track to Sign O' the Times. It was seemingly never considered for any album project during the era.

"Soul Psychodelicide"

Though it was namechecked by Prince on "Joy in Repetition" (intended for Crystal Ball but included on the Graffiti Bridge soundtrack in 1990), the epic "Soul Psychodelicide" only gets its first release on this box set.

"The Ball"

Though Prince removed "The Ball" from Crystal Ball to deliver Sign O' the Times to Warner Bros., fans heard a revised version of this track only a year later, when it was given new lyrics and overdubs and became "Eye No," the opener to 1988's Lovesexy.

"Adonis and Bathsheba"

"Adonis and Bathsheba" was another one planned for the aborted second volume of Crystal Ball, imagining a steamy encounter between the son of Greek gods and the Bible's bathing beauty.

"Forever in My Life" (Early Vocal Run-Through)

The last track on LP number one of Sign O' the Times original version, "Forever in My Life" is a sweet and sentimental love song, adored by fans but never released as a single. Here listeners get a glimpse of the tune in its early stages, with Prince strumming an acoustic guitar rendition as he runs through the track. Though it lacks the vocal layering featured on the studio version, the sparse arrangement let's the Purple One's gifted songwriting shine through.

"Crucial" (Alternate Lyrics Version)

According to the liner notes for the rarities set Crystal Ball, "Crucial" was a last-minute elimination from the Crystal Ball/Sign O' the Times line-up, when it was swapped for "Adore." The Sign box set provides another take on the track.

"The Cocoa Boys" / "When the Dawn of the Morning Comes"

Just because Prince collectors are a fastidious bunch doesn't mean the super deluxe Sign O' the Times offers no surprises. Almost nothing is known about these tracks outside of an idea that they were earmarked for an unrealized musical project called The Dawn - a title and concept Prince tossed around often throughout the rest of his career.

"Witness 4 the Prosecution" (Version 2)

Prince was quick to clean musical house after disbanding the Revolution, and one of his first acts was re-recording Dream Factory's "Witness 4 the Prosecution" with an eye to give it to country singer Deborah Allen. (She opted for a different track, "Telepathy," whose composition was credited to Prince alter-ego Joey Coco.)

"It Be's Like That Sometimes"

One of the few songs not known to be bootlegged before the Sign O' the Times box set, this closing track to the second vault disc is one of many welcome surprises.

"Emotional Pump"

Prince gave this demo to his idol Joni Mitchell, but she declined to record it. "I can't sing this, I'd have to jump around in a black teddy," she told the artist. "You think I should be jumping around in a black teddy?"

"Rebirth of the Flesh" (Original Outro)

Before Sign O' the Times hit record stores, Prince planned an album as an anonymous, feminine alter ego named Camille. Every track from that album was released on Sign O' the Times or elsewhere, except the LP's intended opener, finally available on the box set.

"Cosmic Day"

Touted as the deluxe Sign O' the Times set's third single, "Cosmic Day" is among the box's most eclectic and unknown material. (Even bootlegs had only caught fragments of the track.) This psychedelic rave-up recalls the vibe of Sign's second track, "Play in the Sunshine."

"Walkin' in Glory"

Another one of the Sign O' the Times box's more mysterious tracks, "Walkin' in Glory" is said to be a gospel-influenced number, and purportedly Prince's way of atoning for the more risque tone of The Black Album's "Bob George." Ain't that a bitch?

"Wally"

One of the most legendary unreleased Prince songs, engineer Susan Rogers has told the tale of how Prince kept overdubbing this deeply heartfelt track and demanding she erase the tape. Whether this is a second take or a mysteriously preserved version of the first remains to be heard.

"I Need a Man" / "Promise 2 Be True" / "Jealous Girl" (Version 2) / "There's Something I Like About Being Your Fool"

This clutch of songs from early 1987 were never considered for Sign O' the Times, though Prince offered at least one - "I Need a Man," the sixth and final single from the super deluxe edition - to Bonnie Raitt when attempting to sign her to his Paisley Park Records. Meanwhile, "Jealous Girl," from that same session, was previously recorded by pre-Vanity 6 project the Hookers and given to the Bangles for consideration alongside their future No. 2 hit "Manic Monday.")

"Big Tall Wall" (Version 2)

With this fully revamped version of Dream Factory outtake "Big Tall Wall" from 1987, the Sign O' the Times box set turns an eye to the future. Prince considered this for an early version of the project that would become 1990's bizarre Purple Rain sequel, Graffiti Bridge.

"A Place in Heaven" (Lisa Vocal)

Toward the end of the third and final Sign O' the Times vault disc, things rewind back to the Dream Factory era for a bittersweet moment: the final version of "A Place in Heaven" intended for the lost album, with Coleman singing lead vocals.

"Wonderful Day" (12" Mix) / "Strange Relationship" (1987 Shep Pettibone Club Mix)

The Sign O' the Times vault discs close with a nod to the dance floor, with two unreleased extended versions of album track "Strange Relationship" mixed by frequent Madonna and Janet Jackson collaborator Shep Pettibone, plus a fully unrealized 12" version of "Wonderful Day," slated for early configurations of Dream Factory but never released.