I dunno if this was one of those, given that the books were apparently stashed under a floor for all this time. Makes me think it was a speculative theft but they couldn't find buyers.
They might have been waiting for waters to calm down. 3 years is not that much time to wait, for objects of this rarity. In fact, they might have planned to keep them for longer but for covid19 forcing their hand (the black economy must be currently struggling in the same way as the regular one, of course).
