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Indeed, not only me had a different info on that.
Unfortunately I didn't had anymore the 33 to show it here, but it was noticeable less hollow than my 31 & 32s.
In fact, all these razors were...

The numbers are just model numbers. Kind of grind, blade width, points and thumb notches seems to be somewhat random within the numeration.
E.g.: 31 & 32 are full hollows, but 33s are not só deeply...