TLDR: I figured out my own awkward workaround, see below

I'm trying to enter character names for actors in an anthology series (The Outer Limits 1963). The actors are all being added as guest stars for each episode, as suggested in the bible. Before I started editing, some episodes had credits for some or all of the actors, with only a few of the episodes including character names. The majority of episodes had only a few actors (opening titles) listed without any character names.

What I found trying to add character names is that if the actor already existed in the episode (with empty character name) but the actor also existed in more than one episode, then editing the character name changed it for all of the actor's appearances in the other episodes.

It took a while to figure out this was happening (very few actors appear in multiple episodes), but the workaround appears to be to delete all but one of the multiple empty character name entries for the actor (or just delete all the existing actor entries since it is simpler then figuring out how many multiples exist and for which). This does take a bunch of extra time to add/look up each of the deleted actors again, however.

I guess my suggestion is for the UI to have some way to suggest/indicate to the user that if they edit a character field in this case it will be affecting multiple episode entries in the series. I can see why it works the way it does for the most common use cases (a guest actor appearing in several episodes as the same character) but if there had been a way for the UI to tell me I was applying the character name to multiple episodes I would have figured out what was wrong with the pre-existing entries sooner.