No bishop is permitted under any pretext or privilege whatsoever to exercise episcopal functions in the diocese of another bishop, without the permission of the Ordinary of the place and with regard to persons subordinate to the same Ordinary. If any bishop does otherwise, he will be lawfully suspended from his episcopal functions
As regards your comparison twixt Amedrica and the Soviets, if the Vatican were America and the SSPX the Soviets, then for the comparison to be seen as it really exists, the Soviets would have had to occupy parts of Georgia, Maine, Nebraska etc etc
Congratulations, you entirely missed the point of my post!