Factual error: When the hot air balloon comes down with Carrie in it you can see N410AA printed on it. This is commonly called a tail number on planes and is issued through the FAA, which of course did not exist during the time period of the episode.
Factual error: When the man is holding onto the rope from the balloon, you can see modern tire tracks in the field.
Factual error: A modern day fire extinguisher is shown on a beam Charles walks next to in the town of Bixby.
I'll Be Waving As You Drive Away (1) - S4-E21
Factual error: This episode takes place just after Grace was born (1877). Mary would have been 12 during this time frame, but she is portraying a 15-year-old.
Suggested correction: Wasn't Mary the one in the balloon?
Mary was in the balloon earlier in the episode with the man who runs it but near the end, Carrie wondered off into it and it took off with her inside ALONE.