Coley is frequently mentioned as a cheap local fish. Locals confirm that coley was pretty much unknown in Cornwall in 1936 - far more likely would be ling or pollack. Additionally, "starry-gazey pie", of which the fish was to be an ingredient, is unique to Mousehole, about 30 miles from the supposed location in the film.
While Andrea is playing at the local party, another violin appears in the lower right hand corner and is being played at the same time that Andrea seems to be playing, but there's only one violin heard at the time. Could it be that the "real" violinist was captured on film by accident?