I am a score buff and most of my music is what you can call a score music. And your question is something I was struggling for years, changing the rules governing my info storage system; and this is what I have settled on and believe it cannot be done better:
YEAR: the year of first release of the album; not some re-release and not of the premier of the movie or of the recording session
ALBUM: if this is some later re-release ["special edition" or "complete recording session" and such] then I add the year of that release in here [as well as description of it]
YEAR+ / ORIGYEAR [or however you wanna call it or whatever you want to or can utilize]: the year of the movie premiere or recording session- if you happen to that they happened earlier than the release of the movie
PUBLISHER: this is where I put the name of the parties involved with publication of the album
ALBUM ID / DISCNUMBER: this is where I put the number [code] of the release - if I combine this with the PUBLISHER info then I know for sure what release I am listening too
TITLE: here I can store information about the year of the mix or version
That YEAR+ I most often leave empty. As it is often a case when a movie was from 2000, while the recording took place in 1999, thus I always think such when I see "2000" and "score" [I suspect 1999]. It is also not so seldom that the score is released a year later than the movie- but one year
And if it had taken place in 1999 and 2000, then I would place "1999-2000" [if I would take time to check it out]. But if the movie was a remake and the piece is some theme from the original from 1975, then I would use that field for denoting that info by putting "1975". And if there was a combination of "earlier years", I can put "1975; 1999-2000". Or I could just create yet another field to distinct between these two but that kind of situation is rare and I prefer to just use that YEAR+ for years of the first know recording [e.g. 1975] of a song that was later on covered [e.g. in 1999] or remixed [e.g. 2000]. And if that is not enough I can always use the TITLE do be very precise. Theoretically every piece of music from some "special edition" should have such mix info put in the TITLE [along with the year info], but that can be read by me from the ALBUM- to simply put: if the situation does not require it, I do not put year in the TITLE, as it would lead to abundance of very long titles, thus creating overall obscure of the readability
Of course I say "movie" but mean also series, videogame, stageplays and others. And rules for OSTs are the same- but even easier, as there is rather no cases of remastered OSTs or theirs special edition- and if there is more than one I can always put a number to it, counting them onward from the very first one [although in the world of anime that could be unfortunately a higher level math]
And of course there is the issue of a given player abilities to display less popular or made up fields and / or of signs like ;. I for sure had to start using COMMENT instead of the legit ORIGYEAR or made up YEAR-ORIGINAL, because Advanced Title Formatting in Winamp would not see them or display them wrongly for some or all of the audio file formats that I use. You can read rather thoroughly about it here:
But all in all I always viewed such issues in such way: there is precise managing of at in Mp3tag and there is the display of that data outside of it [that may suffer from various restrictions]