At minute 20:30 of the video link, Fr. Pfieffer shares his stance on this topic(there are a lot of things that are worrying about his response).
I have seen video of the St. Andrew 1945 missal in Fr. Pfeiffer's hands during a sermon, and also the Fr. Lasance pre 55 missal. I have asked Fr. Hewko and Fr. Giroard about St. Joseph being added to the canon. Fr. Hewko uses the 62 and follows Abp. Lefebvre policy that there is nothing wrong pre V2. More alarming is Fr. Giroard(who I am fond of); he told me in email that he likes St. Joseph being added to the canon - so he uses the 62.
When I met Fr. Pfieffer, our discussion(30-45 minutes) was about geocentrism and the errors of Pius XII. I am quoting Fr. Pfieffer who initiated the subject, saying to me "nobody wants to talk about the errors of Pius XII". He recognizes that Pius XII's approval of birth prevention is not traditional(I add or catholic), but he does not want to do the math(the ghost of abp. Lefebvre might haunt him for departing sspx tradition).