itunes-trying to remove dup songs individually

mac book pro user, itunes v 12.4.3.1 (unable to update presently)

i have a ton of dups since i didn't know itunes auto kept copies each time i added something (i HAVE changed that), but i still typically have anywhere from 3 up to 6 versions of a song. i've found that some versions play quieter or louder of others (or 1 version has comments or rating i want to keep), so instead of using find duplicates, i list library by songs in alpha order, play each version, & then delete & move to trash the ones i don't want. when i reopened my library, there are a TON of versions i kept that itunes can't find. fortunately i've only deleted songs beginning with 'a' and a few 'b's', but HELP!!!