I suppose there is some merit to that argument. It seems to me, there are several different “categories” of SSPX Mass attendees (can we agree on that term?): 1. Their priests, who are illicitly offering sacraments, despite being suspended, would probably be the least likely to qualify as Knights, since they are knowingly acting contrary to the directives of the Church; 2. Those married by, or who confess to, SSPX Priests - there’s an argument that they may not be “practical catholics,” but I would say that depends on whether they know about the status of these particular sacraments. And would it make them non-practical Catholics, or simply in a state of mortal sin at the moment? However, the big question is, what about the third category: Married prior to attending SSPX Masses, confess to any available priest (SSPX or otherwise), but regularly attends SSPX Mass on Sunday and Holy Days of Obligation?
I still say it’s a good question for the Supreme Advocate.