Only if you're dogmatic about the matter one way or the other.
 

I don't think there's any reason or right to know, ESPECIALLY when it means absolutely nothing when an SSPX priest SAYS it

So the "faithful" who attend can also pretend they're really in union with Prevost and Martin when they're actually not?  To me, worse than simple material error in inserting the name would be that it basically is a LIE in the middle of the most sacred prayer in existence.

If I were a priest, I might say "una cuм famulo tuo papa nostro" but omit the name, since to positively assert that Bergoglio and Prevost are to be numbered among those "orthodox cultivators of the Catholic and Apostolic faith" ... well, that's just a blatant lie and does not belong in the Canon for that reason, whether or not you think they're Popes, since they're most certainly not orthodox cultivators of the Apostolic faith.  In fact, being "Traditionalist", the whole point is that you do NOT consider them to be orthodox cultivators of the Apostolic (aka Traditional) faith, right?  It's just a stupid lie that I could never say with a straight face, not in the middle of the most sacred prayer every offered to God.