Saved by the Bell series from 1989 and 2020 are being mixed

I’d definitely check the edit on the library - not the collection - to see if “prefer local metadata” is enabled. I disable that in case I messed up the metadata listings.

I would also try the Plex Dance. Even with the name changes, sometimes without some cache clearing it doesn’t pick up the changes.

If none of that works it might be a mismatch on the Plex Agent side of things. Which agent\scanner are you using?