Following your faulty logic, of course, Gregory would not have legitimately codified the Rite around the year 600, and Quo Primum was some sort of artificial construct based on legerdemain, trickery, and deceit.
Yup.
Codifying rites does not mean creating them out of whole cloth--by a committee of humanists no less. Codification simply makes more permanent what had already evolved up to that time--under the guidance of the Holy Spirit.