Revealing mistake: In a few UNIT stories you can see where BBC TV badges have been on the UNIT land rovers.
Other mistake: In every William Hartnell title scene there is a point where it tells you that you are watching "DOCTOR OHO". It lasts for three seconds and is probably the result of a lazy FX team as the left side is a mirror image of the right.
Answer: It was never destroyed on-screen; it was intact at the end of the TV movie, and destroyed by the start of the 2005 series. It was destroyed in the novel "The Ancestor Cell," but in a completely different manner to what happened in the series.
DaveJB