Merrick's safe has a dial with sixty numbers on it, and three combination numbers. However, on the inside there are only four single-digit numbers on the tumblers. It would be impossible to dial three two-digit numbers given that.
When Barney climbs back onto the window washer platform he leaves the blinds down but open. The two windows on either side have closed blinds. When the scene cuts to a wide shot there is no window with open down blinds.
When Barney is hiding behind the see-through mirror in Stone's office, he is fully illuminated. In reality he would want total darkness on his side of the mirror glass in order to not be seen from the other side.
When Barney goes through the window into Stone's office, the window washer's platform is seen going back down in the next shot. Those platforms require 2 operators to move yet there was only one person left on the platform. They have carefully cropped out the other end where the extra person is operating the left lift motor to descend.
When the crossword puzzle is shown in closeup, it is clear that aside from the word being entered and the words immediately surrounding that entry, the letters entered are gibberish.
It is not explained if the blackmail is indiscretions committed by honest government officials to be used in the future, or if it is for keeping corrupt officials in a vise hold as they do the bidding of the syndicate.