During the classic first Tennant era episode School Reunion there’s a detail that is technically correct, however it is only inadvertently correct.

When the Doctor and Sarah Jane first encounter each other, they exchanged the following dialogue:

SARAH: It's you. Oh, Doctor Oh, my God, it's you, isn't it. You've regenerated. DOCTOR: Yeah. Half a dozen times since we last met.

Now, back in 2006, this was technically correct, as from Baker to Tennant, that was 6 regenerations e.g.

1: T.Baker to Davison 2: Davison to C.Baker 3: C.Baker to McCoy 4: McCoy to McGann 5: McGann to Eccleston 6: Eccleston to Tennant

There we have it: 6 regenerations, half a dozen exactly, and everything fit nice and snug…

Then came the War Doctor, and messed everything up 🙄.

The inclusion of the war doctor in 2013 (first appearing in the Name of the Doctor) adds another regeneration to the list, thereby breaking the Doctor’s assertion of half a dozen. It’s still close, but not quite exact. So you’d think this breaks what the Doctor said, right???

Wrong.

The fact is, there’s one detail that actually makes this statement true: the five Doctors.

Most people are assuming that when the Doctor says this, he is referring to her travels with Tom Baker as ‘the last time we met’. However, the last time the doctor and Sarah Jane met (in the mainstream show, at least; we’re not counting comics/audiobooks which completely blow this all out anyway from all angles) was in the 1983 classic The Five Doctors. And what was the latest incarnation the Doctor was in at that point? His 5th: Peter Davison. Hence, the last time the Doctor and Sarah Jane met was when he was already in his 5th incarnation and had already gone through his initial regeneration. In fact, Tom Baker famously wasn’t even in the episode, aside from a minor extra-footage cameo. Revising the list, we can therefore see that the Doctor’s assertion holds correct.

1: Davison to C.Baker 2: C.Baker to McCoy 3: McCoy to McGann 4: McGann to War 5: War to Eccleston 6: Eccleston to Tennant

Interestingly enough though, this minor detail technically only makes the statement true since 2013: before 2013, there was no War Doctor and Toby Whitehouse (the writer of the School Reunion episode) and RTD had no way of knowing that Moffat would eventually create the War Doctor, but they also never factored in the Five Doctors to that comment at the time, which is a surprising detail to miss as it technically would have made the assertion incorrect if not for the creation of the War Doctor. If they had, then technically there would’ve only been 5 regenerations since — again, a close number, but still technically incorrect:

1: Davison to C.Baker 2: C.Baker to McCoy 3: McCoy to McGann 4: McGann to Eccleston 5: Eccleston to Tennant

What a strange inadvertent occurrence.