I was just watching the II scene where Roth tells Michael that the "$2 million never made it to the island." How did he know that? Then, in the very next scene, Fredo drives carrying the the $2 million. Roth knows that also.

Now, besides the obvious question about how Roth knew anything about the $2 million's location, why did Roth conclude (rather plaintively) that the $2 million never made it to the island and why didn't Michael simply tell him that it was on its way?