Unmerging is, unfortunately, messy and difficult.
My suggestion is to start by identifying one recording for each version that can be unambiguously determined to be that version, and add disambiguations to each. (I see you’ve already done that for the 1999 version.) Treat the existing merged version as whatever appears on the largest number of the releases it’s currently linked to - I’m guessing that might be the original 1980 version?
The tedious part will be going through all the releases that currently have the erroneously merged recording and re-linking them to the correct one.
The merged recording has a lot of acoustids attached, some of which likely belong to the other versions. If you can match those definitively to a specific version, unlink them from the merged one.
I second what highstrung said. We need new recordings with clear annotations and disambiguations to let editors know different versions exist and they shouldn’t be picked erroneously. Usually we try to salvage the original mess into the most common recording, but sometimes it’s turned into a “catch all” for unknown versions if it’s too tedious to try and use it for anything besides a bucket of unknown recordings. I’ll try to help you with this effort.
After working through this some, the original mess isn’t as bad as I expected. Luckily the 1999 version is 20 seconds longer which makes it easier to identify. As far as I can tell the majority of the tracks on the original recording are indeed the original 1980 recording. I’ve modified a handful of releases and confirmed a few more. I’ll continue checking as I can and adding to the annotations as necessary.
I forgot to add this- It does seem a tad difficult to distinguish the 1980 recording and the 1990 re-recording. I’ve been listening to the vocals between 0:34 and 0:40 where Kim Carnes’ voice is much louder and raspier on the 1990 re-recording versus softer on the original recording.
Thank you both for your responses! Sorry that I’m late getting back to you.
The back story is that Rogers/Carnes re-recorded the track (twice) because the original label wouldn’t grant permission for Rogers to use their original studio recording on a new compilation album. The 1990 re-record was released on his ‘After Dark’ album, and the second re-recording was originally used on a Greatest Hits/Best Of collection.
@agatzk I see you’ve already spotted this and made edits accordingly. I’ll have a trawl through everything shortly, but I think you’ve sorted it all!