The Letter - S5-E7
Factual error: Sgt. Saunders is looking at a color photo of his kid brother in a letter from home. Aside from being prohibitively expensive for the average family to afford, color photos were not common. Also, the wartime rationing of photo chemicals for color film used by civilians would not be available.
The Return of Golden Tom - S4-E25
Factual error: The Tedlers' kitchen is a 19th Century redress of a 20th Century set, but still includes a modern sink and faucet fixture where a water pump should be.
Factual error: In the opening scene, the Clampetts are driving home from Malibu. From Malibu to Beverly Hills is east. But as they head home, the ocean is on their left, which means they are driving west.
Water's Edge - S3-E3
Factual error: Pete Taylor's corpse is a bare skeleton after just two years in the sea-shack's attic, though it shouldn't be. There should at least be traces of hair and clothing surrounding the bones. (00:40:00)
Factual error: As the robot bird approaches Earth, South America is the wrong way around.