Hardcore Traditional Catholics: What is the difference between the Pius V Tridentine Mass and the 1962 one?

A very conservative priest says Mass at a local independent chapel- not attached to our local dioscese- says the 1962 Tridentine Mass is not the same as the original Tridentine Mass of Pius V (circa 1500). (They only say the Pius V Mass at this church and believe the later Masses such as the Novus Ordo are invalid). What changes have been made? Pre-1962 Missals are very hard to come by and I wonder if it just a matter of the English rubrics, or translation of the Latin. They don't seem to be entirely in line with the Pope on this matter. Does this make this chapel and its community of worshipers technically Protestant in some weird retro way? Thanks for your opinions.