Factual error: When Holmes gets rundown by the carriage, he gets taken home and Watson ministers to his head wound. Holmes gets up a short time later and refers to the carriage as a hansom, which is a little two-wheeled cab. The attacker drove a brougham, with four wheels and four-in-hand horses. Even with a slightly bruised head, the master of observation would never make this simple yet telling mistake as he's shown seeing the carriage. The type of carriage is vital to the plot later as it suggests the wealth and status of the murderer and it appears to be used to commit the crimes.
Murder by Decree (1979)
1 factual error - chronological order
Directed by: Bob Clark
Starring: Christopher Plummer, James Mason, David Hemmings, Susan Clark
Revealing mistake: At the end, when the inspector is stabbed by one of the murderers, he falls back into a sturdy looking fence that breaks apart. As he is lying there, you can see the pre-cuts on the wood so that the fence would break cleanly in a specific spot.