I'm pretty sure we find out Elizabeth's maiden name is Mitchell in the episode where her parents come to visit. I could be wrong about the episode, but it was known.

We never find out who was the source of the leak though.

I never get how Mozzie and Neil end up with cars. In the episode where the Burke's neighbors are thieves, the duo are on a stakeout across the street. There are a few episodes where Mozzie randomly has a car too.
This is a bit unrelated but every now and again, we learn that Neil can shoot yet we never find out how…