Board Thread:The Panopticon/@comment-1451563-20180913002703/@comment-6032121-20181001174234

Ben Moore512 wrote: (…) this wiki does take into account out of universe things from time to time. It counts Dreyfus’ Master as the first incarnation, when all we have to go on that is the news article announcing the set he was in.

So really, it doesn’t matter much if it’s only out of universe, because this wiki likes to use that sometimes. I think the Dreyfus Master is a rather different issue. It's evidence of authorial intent for a narrative element.

On the other hand, the fact that out-of-universe content refers to the Doctor as "they" here (and I'm not entirely sure this was a singular "they" as opposed to another "wonderful chap… all of them"-type gag) doesn't say much about whether this is how characters would refer to the Doctor in-universe.

Regardless, while Tardis Wiki occasionally uses out-of-universe sources, they are to be taken with caution (as they are technically disallowed by Tardis:Valid Sources, being non-narrative), and are secondary to in-universe sources.

So I think Game-Fanatic's point is that for now we have evidence of the "he-she switching" in-universe, and of "singular they" only out-of-universe; hence until such a time as "they" proves itself to be a valid in-universe alternative, we should go with the in-universe take over it.