Professor Zoom wrote:
I'm personally not all that convinced Kate was lying in TPOT; I reckon she genuinely hadn't met Eleven before then. But then we also know that history can be changed. Perhaps in a subsequent adventure, the Doctor went back in time and met Kate earlier in her personal timeline, explaining how she might recognize him in DOTD?
That's your explanation right there. In Doctor Who, history is ALWAYS changing. But, the BBC can't afford to reshoot the episodes to reflect the altered timeline...
It's possible that's why nobody now remembers Britain's manned expeditions to Mars and Jupiter in the 70's; they were erased from history in unseen adventures. I believe some people have even speculated it could explain the UNIT Dating Controversy, but I'm not too sure about that.
This kind of approach might even help with a number of discontinuities in Star Trek. Just look at stories like DS9 "Past Tense", First Contact
, and the Temporal Cold War in ENT.