Other mistake: The tenant board member tells George that Mr. Eldrige in apartment 8C has decided he wants the new apartment. However, the new apartment in question has a 3-digit number - 808 I believe. This indicates that the building would not have single digit numbers and letters (Such as 5E, 8C, etc.) as part of its numbering system.
The Man in the Long Black Coat - S2-E8
Other mistake: Eric Idle is called Dr Melvin Whale, but according to the subtitles he is called Dr Melvin Mile.
Did the Earth Move For You? - S2-E1
Other mistake: Viv and Phil are waiting in his office for the power to come back on after the earthquake, but you can see lights on in the building across the street. (00:16:30)
Life's Ruff - S1-E20
Other mistake: Despite Hip peeking from the girder, he cannot be seen behind them. This also happens to Hop shortly after when they are pulling the astronauts behind there. (00:09:06)
Dawn and the Haunted House - S1-E2
Other mistake: Dawn looks directly at the camera right before Stacey and the kids tickle her.
Safety in New York (or, Bertie Sets Sail) - S3-E1
Other mistake: When Tuppy goes to turn off the burglar alarm for Wooster, it's behind a hidden panel with a sign saying "Alarm Switch" above the panel. Why bother putting the switch behind a concealed panel if you're then going to label it? (Unless you're doing it for a viewing audience). (00:35:00)
Other mistake: When Fay is talking to Lowell over the walkie talkie, when she is giving him the recipe she is not pressing the button to talk, but Lowell still responds.