Throughout the film the frizzens were often open and the flashpans exposed on the supposed flintlock pistols and muskets, but the guns fired anyway. These were obviously stage guns, but as a factual point the frizzen must be closed on the pan and there must be a poof of smoke before a flintlock gun will fire.
As Jim Hawkins is climbing down the mast rigging after shooting Israel Hands, the ship is shown adrift and moving toward the shore. But in the overhead shot looking down toward Jim, there is no indication of movement seen in the water below and the ship appears to be stationary. Later, when Long John Silver and Jim are being rowed out to the ship, at least one shot of the two in the row boat's stern similarly shows no sign of the boat moving through the water, but merely floating in place.
The goof item below may give away important plot points.
When Jim discovers the conspiracy, the comment is made that the Squire's party consists of nine people as compared to twenty pirates on the ship. This can be seen when the ship is towed in by the rowboats - thirteen sailors in the rowboats plus six to eight on the ship. However once the party lands and the conflict begins, there is a discrepancy in the numbers. Five or six pirates die during the assault on the stockade (mentioned in the film), two are killed on the ship (Haggot and Israel Hands) and six die when searching for the treasure. This gives a total of fifteen maximum (including Long John Silver). Five pirates have disappeared.