Well, the requirement for seminarians to adhere to the CT is at least since Feb. 2022 (which is after Father died). See @ minute 4:
Just a clarification, if you listen at the minute 4, Bp. Sanborn is speaking of priests who are received into his Roman Catholic Institute. He requires priests who go into his Institute to adhere to the Thesis so to prevent divisions within his Institution.
Bp. Sanborn's policy regarding admission to the seminary has not changed. The Thesis is taught at the seminary, not as a dogma, but as a theological opinion. Seminarians are not required to adhere to the Thesis, but they cannot be members of the Roman Catholic Institute and they must be affiliated with an approved group in order to be ordained.
For many years, Bp. Dolan sent seminarians to MHTS to be trained and they would be ordained by Bp. Dolan. Most of the priests affiliated with SGG went to seminary at MHTS, including Bp.McGuire and Bp. Nkamuke. Fr. Cekada used to come to the seminary monthly to teach.
If you start this video at the 11:07 mark, Bp. Sanborn explains his position.