Factual error: When they go to 1954, the hamburger drive in says it has frappes. Not invented till '57, and not in the US public eye until at least 45 years later.
Suggested correction: What you're describing is a Greek café frappé made with instant coffee. In New England "Frappe" is what many would consider a milkshake with ice cream in it, and has been around since at least the 50's (Vic's dad even mentions getting frappes in episode 4).
Factual error: The fly Good Chucky kills bleeds red blood. Fly blood is usually clearish with a yellow and green tint. Not opaque red.
Factual error: At the end when Skeksis enters the crystal chamber, in the overhead shot you can see 22 arcane symbols around the crystal when there should only be 18, one for each exiled skeksis. (00:45:53)
Factual error: Despite taking place in Massachusetts and many of the cars having Massachusetts license plates, none of the vehicles has the required annual inspection sticker on the lower part of the passenger side of the windshield.