When Bart comes to hire Benjamin to set him up he throws the bunches of banknotes on the desk and they land in one nice pile. In the very next scene one of the packets is off to one side, however in the next scene they are in a nice pile again and no one has touched them in either scene.
Benji couldn't have been listening to the woman at the gallery who mentioned the Senator "swooshing down the slopes" since it was established he was tied up in the car at the time. It is possible that he heard it if Jackie taped it, but it was never revealed that she was recording at the time.
After it's established that Alister Becket's birthday is March third, Benji remarks that it is six months passed (or six months away). Earlier, however, when scouting the scene of the crime, he looks at the desk calendar and sees that it's mid-October, so really Becket's birthday was less than five months ago or away.