Some artists have released career and genre-defining albums from Dr. Dre's "The Chronic," Nirvana's "Nevermind," Radiohead's "OK Computer," to Weezer's "Pinkerton." Some albums became noted for their adherence to a single theme or narrative, while others are a series of hits after hits.

Then some albums were announced but were never actually released. Regardless of the reason, these works have gained their reputation for being the music industry's lingering what-ifs? Here are four of the famous albums that never saw the light of day.

"Dream Factory" by Prince and The Revolution

This album is said to have been recorded between the Summer of 1982 up until July 1986. Prince's band "The Revolution" was invited to contribute to this supposedly upcoming album. By June 1986, the "Dream Factory" had grown into a 19-track double-disc collection, with songs continuously added and discarded.

Surviving tracks of the "Dream Factory" were incorporated into a new project, "Crystal Ball," intended to be a three-LP release. However, Warner Bros, Prince's distributor, rejected the massive project and whittled it down into a double album we now know as "Sign O' the Times," recognized as among his best works.

"Cigarettes and Valentines" by Green Day

The 2000 Green Day album, "Warning," was supposed to be followed by "Cigarettes and Valentines," which was to be released by 2003. From July to October 2002, the band recorded songs for the albums and were close to completion. By November, the master tapes of their recordings were stolen from their studio. Instead of re-recording the tracks for the album, the trio of Armstrong, Dirnt, and Cool decided to start with new material. They wrote new songs and recorded what became the critically-acclaimed punk rock opera "American Idiot."

Green Day did recover the master tapes for "Cigarettes and Valentines." They used and reworked the songs in the tapes and were included in their other works - some songs were B-sides in the "American Idiot" singles while others were re-recorded for the last of their triple project, "¡Tré!."

"Songs from the Black Hole" by Weezer

In 1994, Weezer released their eponymous debut album, better known as "The Blue Album." Critics praised the songwriting, and the album itself spawned hits such as "Buddy Holly," "Say It Isn't So," and "Undone - The Sweater Song."

After achieving mainstream success, frontman and lead songwriter Rivers Cuomo planned a rock opera reflecting his mixed emotions about their newfound stardom. The band members Brian Bell and Matt Sharp were set to provide additional vocals. The band had recorded demos for the "Black Hole" by 1994.

However, as Cuomo started at Harvard University, his songwriting grew to be darker and more introspective - a fact to be highlighted by their next release, "Pinkerton." Cuomo started to see "Songs from the Black Hole" as "too whimsical." The rock opera was scrapped, "Pinkerton" was released, and two songs from the abandoned work were included in the new release - "I Just Threw Out the Love of my Dreams" and "Devotion."

"Black Gold" by Jimi Hendrix

The "holy grail" of all Jimi Hendrix collectibles, the 1970 recordings of the iconic guitarist supposedly contained 16 songs recorded only with his vocals and a Martin acoustic guitar. In a March 1970 interview with Rolling Stone, he shared about saving more time for himself "where I could do more writing." He described some of his works as "cartoon-type material," reflecting his intent at writing songs beyond the convention. 

Jimi Hendrix presented his numbered cassette tapes to drummer Mitch Mitchell, who promptly forgot about the original Hendrix recordings even as the prolific musician died in September of that year. For 22 years, the cassettes in a box labeled "BG" remained untouched. The world thought they were stolen or lost and even doubted if these recordings even existed.

In 1992, the mystery of the "Black Gold" was solved when Tony Brown, a Hendrix biographer, and avid collector, interviewed Mitchell. He found that the drummer had all cassettes in the original box, and even the Martin acoustic guitar Hendrix used for the recordings. In 2010, Janie Hendrix said that "Black Gold" will be released "this decade.