[user104658]

There has at some point been a throwaway line about timelords "revisiting old faces" - I couldn't tell you when or which doctor said it, for some reason I think it was Matt Smith - but the suggestion was definitely that it sometimes happen. They may have thrown it in there as an easteregg to refer back to should they ever recast an old incarnation. E.g. They introduced the idea that changing sex on regeneration was possible quite a while before actually doing it.