What a great thread idea, there's so many worth noting! Glad it's been revived. Here's a few of note: The Very Best of Badfinger (2000, Apple/Capitol) uses the unreleased 'original' recording of "Name Of The Game" (which was issued as a CD bonus track in 1991) rather than the released 'second' version, which is a different recording entirely. The preceding track on the disc, "Baby Blue," is also the dry album mix rather than the more famous U.S. single mix with extra reverb. The album version has always had a clipped intro as well, which went uncorrected on this compilation (or ever!) The Kinks' Anthology 1964-1971 was advertised as having a (first-time) true stereo mix of "Dead End Street" (and says so on the box), but on the disc it merely has the regular mono mix. The stereo mix intended for this did later come out on the 2016 LP The Best of The Kinks 1964-1970, but the mix remains unavailable on CD or digital. The Zombies' The Zombies' Greatest Hits (Varese Sarabande, 2018) claims to be mostly mono single versions except for certain tracks in stereo (per its back insert), but the disc is actually *entirely* mono single versions, even on the songs it marks as 'stereo' on the back! I believe that means this is the only CD where one can get the mono mix of 'Time Of The Season' besides the several CDs with the mono Odessey and Oracle album (assuming that the album and single mixes are identical? Someone else may be able to confirm!) Chad & Jeremy's Painted Dayglow Smile (A Collection) uses a totally alternate recording of "I Don't Wanna Lose You Baby," though the notes only indicate it being a new stereo mix of the regular track. However, the Sundazed remaster of the "I Don't Want To Lose You Baby" album has one bonus track - an 'alternate version' of the title track - and that recording is another completely different scratch recording of the song. So there are *three* finished versions (with different arrangements, overdubs and vocal takes) of the song floating around...! This same C&J comp also boasts having the '45 version' of "Rest In Peace," but it is merely the stereo album mix (the booklet does have the correct running time for the album mix, which makes it an evident giveaway: 6:49 on the album compared to 3:19 on the single!). It also has a number of first-time stereo mixes of songs from 45s (which remain the definitive, and often only, versions available on reissues - the mono originals evidently phased out). The last track is 'Sister Marie,' which the booklet strangely claims is both the '45 version' and also a 'previously unissued alternate take' in the same sentence (not sure how that's possible??). It's definitely the same take as the single, but it is a vastly different mix for sure! This version has not appeared anywhere else since this 1992 disc. The Creation's "Painter Man" was only issued in mono upon initial release (as far as I can tell), but a true stereo mix was made somewhere along the line - or two? The various artists' releases Rhino's History of British Rock/British Invasion Vol. 4 from 1988 and Grapefruit's A Slight Disturbance In My Mind: The British Proto-Psychedelic Sounds of 1966 from 2017 both feature true stereo mixes of the version on the single. But the two Creation releases Action Painting from 2016 and Creation Theory from 2017 use a true stereo mix of a completely different (and inferior) take of the song! The Grapefruit release attributes their version being taken from the 2017 set, which is seemingly impossible since the correct version isn't present in the latter set! On the Grapefruit kick, the remastered/expanded version of Neil Innes' How Sweet To Be An Idiot uses both the album version and the single version (two separate recordings) for the first time, but accidentally switched them up - the single version plays during the album and the album version plays in the singles half of the disc! I ripped it to iTunes anyway so it was an easy file-switch, but surely more of a pain for those listening on a traditional system. At least both versions are present, and in great quality! I have more instances worth sharing, but will save them for a later post - this is getting intense!