Continuity mistake: During the robbery, the taxi driven by Danny Green changes from an Austin to a Morris Oxford and back again. Both types are the same colour, but the Austin is the one with the rounded radiator grille, and the Oxford has a flat radiator.
Revealing mistake: During the scene where the gang attempt to catch the parrot, One-Round gets his legs stuck in a chair and falls over, breaking the chair in the process. About a minute later Herbert Lom breaks the record and it cuts back to One-Round, and the exact same shot of him falling over is seen again.
Continuity mistake: After dropping Harry from the bridge, during the short shot of One-Round, a train appears on the tracks behind Marcus and Louis. (01:21:35)
Continuity mistake: Before the 2nd drawing of matches, we see a closeup of Louis' hand and can see that the leftmost match is a long one. The shot then changes to show Harry picking a match, he picks the leftmost one, but it is short. (01:13:25)
Continuity mistake: Before Louis gets out his knife to cut the match, the ashtray is in the middle of the table and the hat is at one edge. Afterwards, the items have swapped positions. (01:02:20)
Factual error: The Boccherini string quintet is actually scored for 2 violins, 1 viola and 2 cellos, not the crooks' line-up of 2 violins, 2 violas and 1 cello.
Suggested correction: I don't really know anything about how string quintets (or quartets) perform, or how any group of musicians might prepare to perform a well-known piece composed many years ago. So maybe my answer is not valid. But would it be acceptable within the music community for a musical group to re-score a piece, so long as they remain faithful to the original? If two members of a string quintet said they were more confident and capable on a viola than on a cello, would the quintet re-score the piece accordingly? Is it acceptable for musicians to adjust a long-established piece of music? Another possibility. The crooks are not musicians at all. They pretend to be musicians, but this is only a "front" for a bank robbery they are planning. They maintain the pretence by miming to records. So is this a subtle joke?"Look, the crooks are pretending to be musicians, but they are getting it all wrong! They are playing the wrong combination of instruments. Ha ha!"
I asked a friend who belongs to a string quartet if you could re-score a quintet piece. She said this would be complicated, difficult, and more trouble than it was worth. So I must retract my suggestion that the crooks re-scored the Boccherini String Quintet. But maybe I am right with my other suggestion. The crooks are not musicians, but only mime to records. Thus, they use the wrong combination of instruments. This is therefore intended as a subtle joke.
