The Warlock's Lurker In The Deep patron in their UA certainly hit me as far more Explorer's Guide To Wildemount than any other potential book... seeing as how one of the PCs in the Critical Role game was an actual warlock with a kraken patron. Now maybe its appearance in UA was just a coincidence and had nothing to do with EGtW... but that seems fishy to me (pun intended.) So I don't take it on faith that all UAs are written and designed for only one specific book and if they aren't selected then they're gone. Especially considering most of the themes can easily be updated and moved from book to book depending on their needs.