If you follow the current timeline, it should go-
Hurt->Eccleston->Tennant->Tennant->Smith->Capaldi->Whitaker->Tennant->Tennant/Gatwa
Hurt was the real 9th doctor, but we call Eccleston the 9th doctor. And (if I get this all right) Tennant regenerated as himself twice, so he should be the 11th, 12th, 15th and Doctor 16 and a half. But people call him the 10th doctor. And Jodie Whitaker should have been the 14th Doctor, but people call her the 13th Doctor. And then Tennant came back and then there was the bigeneration of him and Gatwa.
And just to add to it all, there’s also a female clone of Tennant out there somewhere.
Is anyone else as confused as I am?
EDIT: Oh god, I just realized it gets even more confusing because now there’s all the Doctors before Hartnell.
In the anniversary series “Once and Future” the Doctor, zapped by a new weapon during the Time War, is being haphazardly “de-generated” through a bunch of his own incarnations, past and future, with their attached knowledge and experience, and at one point
spoiler
in the persona of the Eighth Doctor he says “I get the sense the numbering system breaks down after me” and shrugs it off as unimportant.