As seen on the 50th anniversary, Kate Stewart (or the Zygon who looks like Kate Stewart) told Clara that she has a high level of clearance from her previous visit (and photos are shown).
At the time, it was thought that the photos were from a future episode, however, now that Clara's and the 11th Doctor's era are long gone it's never really clarified how she got that level of clearance or when were the photos taken, at least on the show.
Is it ever explained in any other form of media such as Interviews, comics or books or it's a plot hole?