I’ve noticed that if I label 2 files with the same season and episode number under a TV show, plex will display the first one it finds, and ignore the next. Perhaps this makes sense under the theory that there would be no reason to have multiple files of the same TV episode. But there are plenty of reasons one might have multiple files of the same season and episode of a TV series, and would want to have easy access of playback of both files from plex.
For example - the bluray set of the first season of I Love Lucy contains 3 versions of many episodes. An original airing version with original intros and commercials from the first airing, an original rerun version with different openings and commercials, and the standard versions that have been rerun since those original airings. Perhaps it’s a bit redundant to have 3 versions of the same thing - but I’d like to have at least 2, there are enough differences between the original airing and original reruns that having both show up, and picking between the 2 on multiple viewings of the same episodes would be a nice feature. Also - it makes no sense for plex to completely ignore and not make accessible all the content of a person’s files, this seems to have been an oversight, as I can think of several other reasons one might have different versions of the same episodes.