Saving Collections in Gallery
I've never really did this before, so I have no idea if it has always been like this or not. I like collecting in the Sims 4 and a while back I decided to work constantly at trying to get every type of kid's drawings from the art table and paintings in the painting career (and get them to masterpiece levels if possible). The save got old and odd glitches happened, so I decided to save all of the progress onto my gallery and start a new save with the same Sim I had been using. Putting the saved "art studio" down, I was ready to get it going again... only to find that all the paintings no longer had "Made by: [Sim's name]" when hovering my mouse pointer over the works.
I was also sad to find all the fish they caught were not saved. Even in an effort to keep them by placing each fish on the floor, immediately saving them in a room and loading that resulted in the fish all being 1kg and not the unique weights I had my Sim work so hard to catch. They, too, no longer had "Caught by: [Sim's name]".
So, is it supposed to be like this when you try to keep your collections?
You'll always lose the tags such as Made By, Caught By, etc. when you save to your library. Anything connected to a sim like that will be lost too like university diplomas and the like. The item will be there, but the connection to a specific sim will be gone. It's always done that and is just the way it works
It also happens for other things. For example, if upload a lot to the Gallery or your Library that has all the upgrades done, all of those will be gone when you place the lot from your Library/Galley the next time, so you have to do all of them again.
Hope this helps.