Adding missing metadata in folder/file names

[TheDreadPirate]

If you backup the correct folders, ensure that all the media is in the same place when you restore, and correctly restore Jellyfin you shouldn't have to re-identify anything. I've had to restore 3 times due, once due to hardware failure, another for hardware upgrade, and a third time because I borked my OS.

All three times I restored and it was like nothing happened.

But, to your question, you should be using TMDB IDs. Jellyfin makes little or no use of IMDB since access to their API is horribly expensive.

You could experiment with adding the TMDB ID to the folders now and see if Jellyfin keeps existing metadata and watch status. In my experience, Jellyfin usually doesn't purge old metadata right away when moving stuff around.