Now, Vader’s lightsaber being retrieved from the exploded DSII would definitely need a good explanation. Doesn’t it fall down the ractor shaft when Luke cuts off Vader’s hand?
It is about the same as Luke’s lightsabre falling into gas giant.
Weeeell… It goes down a bit pit. We don’t know if there’s a hole at the bottom. It could have just been stuck down there and scavengers found it.