Factual error: A secret file is password-protected on a computer, requiring a six-digit numerical access code. KITT states that the possibilities "are virtually unlimited." In truth, if each digit can be 0 through 9 (numerical meaning no letters or symbols), the possibility is 1 in 10^6, or 1 in a million. A supercomputer like KITT should have no problem running each number systematically until a correct code is found.
Factual error: Disc 2: There is a scene where a cannon shell explodes inside a hospital ward. Everyone in the ward is killed, but there are no signs of limbs torn off or even shrapnel wounds, only some blood here and there. The same thing happens at the Battle of Bull Run when the old woman gets blown out of her bedroom by cannon fire. (01:32:00)
Factual error: Jeweler Albert Harrad calls Laura from his desk phone, but only punches six buttons before getting hold of her office. All U.S. phone numbers have seven digits: six wouldn't have connected him to anything. (00:37:30)
Factual error: During "Jester Balowski's Medieval Torture Hour," Balowski grabs the guys arm and bends it the way arms are supposed to bend, yet you hear a breaking noise.
4 Rms Ocn Vu - S3-E8
Factual error: Some of the visitors came to the Keaton "hotel" (their house) for the "ocean view." This takes place in central Ohio (near Columbus). There are no oceans around there.
Factual error: There is an intercom system in the library that is used by Derek (and at the end, Edward). They try pushing down the buttons to talk (which is normal for intercoms), but then each time, we are hearing Ricky and his grandfather's conversation from inside the car that's outside without using the intercom connected to the house. In the 80s, a house intercom system would not pick up a conversation in a parked car outside.
Lisa's Song - S3-E14
Factual error: Doris finds out that Gypsy Queen "Lisa" died from influenza around 1918, so she didn't get to star in her performance. However, when Doris and Lisa's ghost are singing their duet later, Lisa's hair and costume are 1980s style, instead of the era she died.
Factual error: The forces of Cassiopeia all sport the crown-like "W" sign which is the shape of that constellation... but only as seen from earth! These five points in three-dimensional space (like all star signs named after anything) look like that when viewed from our own planet; but from anywhere else, they aren't shaped like that at all. Why would they chose to see themselves through a very specific angle of view from some other distant planet (earth)?