Theo's hand jumps on and off Paul's arm between shots as they sit at the casino bar.
Hugo has white hair, but when seen repairing the car engine he has dark hair.
When Rod Steiger (Paul) & Michael Dante (Louis) make their escape on the ledge of the casino, their white coats are rubbing on the dirty outside walls. Immediately after, they meet up with Joan Collins in the casino and their white coats are clean.
After the robbery, when they are driving from Monaco to Cannes, they are driving to the east. Cannes is west of Monaco.
The casino in Monte Carlo is not on the edge of a cliff.