Originally Posted by I, Brian
Especially as in the Silence in the Library two parter, she described Tennant's Doctor as looking young - which implied she knew an older-looking Doctor - and certainly not one as young as Matt Smith.
Then again, as Dave mentioned elsewhere, the longer Doctor Who as a series runs, the harder is it for continuity to run smooth.
I like the idea of much longer story arcs. Though I suspect he has no real idea where this will eventually go, it would be good if in say, two regenerations time, an older looking Doctor meets Song just before he does as Tennant. The meeting Queen Elizabeth I line was, I thought, just a throwaway line, but they did come back and address it later.