[edit: too slow; opted to keep my post anyway in case it gives you an additional pointer]
The show should be match ok.
Given your naming my guess is that Plex doesn’t recognize the episodes as belonging to different shows. When checking out the details of your 1985 episodes in Plex, you’ll probably see multiple files assigned to each of them (e.g. via Get Info from the context menu or on the Info tab when editing the episode item) → Plex will treat those as different-quality versions of the same video.
Try to give Plex something to go with and stick as close to the official naming schema as possible, e.gy putting the year the show first aired in brackets.
Example:
tv
The Berenstain Bears (2003)
Season 01
The Berenstain Bears (2003) - S01E01-E02 - Trouble at School + Visit the Dentist.jpg
The Berenstain Bears (2003) - S01E01-E02 - Trouble at School + Visit the Dentist.mp4
The Berenstain Bears (2003) - S01E03-E04 - Mama's New Job + Mighty Milton.jpg
The Berenstain Bears (2003) - S01E03-E04 - Mama's New Job + Mighty Milton.mp4
…
With mp4 files conflicting embedded metadata might also mess things up.