Actually the Jeffries drawings are a bit off too. This is something that has been of major discussion on another forum I haunt. The Polar Lights D7 kit has been released just this last week and there was a major discussion about it being too big. The interesting part is the kit has some of the nicest drawings I have seen, including color schemes and the Romulan variants have a few differences from the Klingon.
As to the Matt Jeffries drawings, I believe the boom to the front part of the ship is just a tad too short. I myself am not really aware of any other drawings.