I was looking for a backdrop I remembered seeing previously and noticed that many previously available backdrops are missing from my character options. For instance, I can select XTGE6 but none of the others that used to be there. There's entire books-worth of backdrops missing from my character options.

Are backdrops just subject to be removed over time or is there some character/account setting I can update to see them again?

This has also happened to me, did this ever get resolved?