Plot hole: Professor Jones says they tried to borrow the cutting equipment a few weeks ago, but Mr. Stevens says it was yesterday. One of them must be wrong...
Plot hole: Jo should know what the dematerialisation circuit looks like. She saw it in 'Terror of the Autons', 'The Three Doctors' and several other episodes.
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