Nope. 650c and 650b are considered the same outside diameter; 650mm. So if 650c is 26” so is 650b.

The b and c refer to the bead diameter; 584mm and 571mm.

650b tires were around before you were born.

Obviously as tires increase in width they increase in height so all sizes are not measured at 650mm outside diameter.

No different from a 700c, (c doesn’t mean clincher), X 23 through 40. They are all identified as 700mm outside diameter, but they all cannot actually measure 700mm in diameter.

John

Edit Added: If you had used etrto 584, such as 60-584, you would have been correct.