The example of the GWS is inapplicable:
1) Precisely because the Church was divided in assenting to the claims of three papal claimants, none of the claimants' "papacies" ever attained the status of dogmatic fact.
There was, at a moment prior to the Western Schism, one papal claimant recognized by all as the true pope. Just because later there were three, does not change it on the grounds Sean posits.
The application of the GWS was to show that there were canonized saints who attended Masses where the wrong pope or no pope was mentioned in the canon. If one were to side with St. Robert Bellarmine in believing that a manifest, formal heretic loses office, they would still be Catholic. They might even be right. But a dogmatic sedeplenist would rather follow a Buddhist pope than admit that an opposing view could be right.
The official position of the SSPX had always been that a formal heretic loses office of the papacy. Indeed, even Bishop Fellay has admitted that it may be possible to say one day that Bergoglio never was pope.
If one were to compile a list of all the people who have doubted the post-conciliar popes on up to Bergoglio, it would be nearly every single Traditionalist priest and bishop (Fr. Gruner, Fr. Kramer, Bishop Williamson, Bishop Fellay, Canonist Fr. Hesse et. al.) on one side and Sean Johnson, Fr. Pfeiffer and the Fraternity of St. Peter on the other.