Other mistake: When Rube is searching the hard-copy (paper) archives, the young man with him opens the last box and pulls out an old "Wanted" poster with Rube's face on it. He tells Rube "This guy looks just like you." Since season 1, episode 1, we've known that Grim Reapers don't look like they did when they were alive (i.e., Millie/Un-George). Yet somehow, Rube has not changed since his life/death.
Plot hole: People who do not have their souls retrieved, before they are killed, will suffer the effects of the death on their soul, eg. the autopsied man has scars and cuts on his soul. So how come the woman who was crushed by a piano (whose soul was only ever retrieved afterwards) is unharmed in soul form?
Continuity mistake: When Rube's talking to the graffiti artist, he's painting what looks like a blue cat. We cut away, hear a brief paint spray, then cut back. There's now far more painted than that spray could have achieved, and what was there already has changed as well.
Factual error: Towards the end of the episode, Mason reads a report on Daisy's death indicating she died 13 December 1938 in Marietta Georgia of smoke inhalation. It apparently was common knowledge that Daisy died on the set of Gone with the Wind (supported in the Halloween episode by someone who knew her when she was alive). The filming of the big fire scene in GWTW was 10 December 1938 so the dates are pretty close. But these early parts of the production of GWTW (and I believe the rest of the movie as well) were filmed in Culver City, CA, not Marietta.
Continuity mistake: At the beginning of the episode George is wearing a sweater that is stained with large blood splatter. During the actual reap she is splattered with blood but the pattern is very different, both in quantity of blood and the splatter locations on her sweater.