[Librarian]

Number theory is already in the name.
Zi-O 2 letters and O.

In all seriousness though, number theory stopped after Wizard.

Number theory has always been off by one digit anyway really. W started it at 2 but it was the 11th series and first of the new decade. So if they corrected number theory with Zi-O, it'd be 10-2 or 20.

So in contrast to build's return to W's 11 approach of 1+1, this would be for the 10+2 people. Or if you want to look at number theory for build as 10, then this is 10 again.