I remember hearing a talk by Fr. Hesse, in which he states that the Archbishop used the 1962 Mass as an act of "self-defense" , by which Fr. Hesse explained that since the Archbishop appeared to be "outside the church" in the eyes of the Vatican hierarchy, he thus wanted to make clear that he and his SSPX do acknowledge that they recognize the Pope as true Popes and one way to show that they mean what they say (and not just empty words),  he decided to use the 1962 Missal of John XXIII. Fr. Hesse then goes on to explain why he uses the Pre-1955 liturgy and excuse the SSPX for not using it do to the "self-defense" maneuver. 

The question for the "Resistance" priests or those not in communication with the Vatican authorities,  does the "self-defense" position still apply, especially if the FSSP and Institute of Christ the king uses it.