When Webster meets Deams and Hector by the ship channel, the wake from a passing ship is seen over their shoulders in the closeup at the end of their conversation. The camera then cuts to a far shot of the same conversational moment, and the water behind them is smooth.
Some versions of this movie being shown on network television has two scenes out of order. There is a scene in which Webster evades the police and then links up with Laura at a party. Then insurance agent Dave shows up at Laura's place to talk to them. After this, there is a scene in which Webster and Laura meet for the first time at a party.
Travis is pulled over by police and is asked for the car's registration. In the 1970s, Texas did not require that the registration be kept in the car, and officers did not ask for it. Hollywood got it wrong because in California drivers were required to present their "registration".
At the house where Laura challenges Webster to break in through the front door, he uses a credit card to jimmy the lock. However, the lock is a deadbolt, and the credit card method is not possible with that kind of lock.
(at around 1h 1 min) The computer printout tells Webster his next chess move is "2-knight to pawn." This is not proper chess terminology as none of the chessboard locations can be designated simply by "pawn". The intent likely is "2-knight takes pawn." (It could be argued the computer programmer made this error, but the programmer would have had to been, or at least worked closely with, a chess master who would know correct chess notation.)
When Webster, posing as a plumber, is casing the Henderlings' house, he makes a quick exit when he sees the real plumber pulling into the driveway; he tells the maid there's a guy coming over who knows exactly what to do. The next scene shows Wester holding a developed picture he had taken at the house. Not shown is the interaction between the real plumber and the maid, especially as the plumber had seen Webster's "plumber" van in the driveway as he pulled in. That conversation likely would have resulted in the police being called.
The jewel thief isn't wearing gloves during his last heist. Even if his fingerprints aren't on file with the police, one would think he might worry about being convicted as the thief eventually via this evidence.