Padre Pio was totally obedient to the Church and the magisterium - during the pontificate of Pius XI (1922-1939) Padre Pio was segregated from the Church; he was forbidden to say public Mass, hear confession or answer personal letters. And he obeyed. Only in 1933 was Padre Pio allowed to return to the ministry.
The older priests were not required to learn the New Mass as it would have been almost impossible. I am at work and in between earning my salary I'll try to find you the documentation on that if you wish... but it only makes sense anyway.
I understand what you are saying in regards to the older priests. I don't need documentation. I trust you. But, it is well documented in some many places that Padre Pio did not have any great love for the N.O. or Vatican II. I often wonder how he would have handled the future given those feelings and his strong obedience to the Church. At this point, it's anyone's guess, although I have read (this article?--can't remember) that one of his spiritual directees maintained strong support for the Traditional Mass and its priests up until her death in the 80's.