Hello Tommy! I reprint below something that I posted on April 24 about this matter of validity which you raise. "Tantum ergo" had raised it.
Hello Tantumergo! And Welcome! Your question, about the "Validity" of Eucharistic Prayer II, is so pastorally important that I think I'd better deal with it instantly.
Unless some priest is such a mad ingenious fool that he decides not to use wheat bread and grape wine, or misses out the Lord's Words at His Last Supper, it is very difficult for him to make a Mass invalid. Even if he were to be a secret atheist! Because of the chaotic situation which arose after Vatican II (but not mandated by the Council) devout laypeople quite often ask your sort of question. If you really want to read all the technical details about what is 'valid' and what is 'invalid' please look back at some earlier posts I gathered together at 4 September 2014; and also read 20 November 2013, 12 May 2014, and 13 March 2015. You see how often people do get worried! I'm sure this will not be the last time I am asked to take up a question like yours.
But my advice to anybody in your position is: Don't worry. Because using EP II certainly does make the Lord's Body and Blood to be present, and truly does offer them in Sacrifice. No ifs, no buts.
Back to Tommy ... the actual words of the form for consecrating a Bishop, introduced in the post-Conciliar Pontifical, had previously been used, for centuries, by Eastern Churches in communion with Rome or whose episcopacy Rome accepted, to consecrate bishops. When this was pointed out to Archbishop Lefebvre, he stopped doubting the efficacy of the rite. As for the Form of Ordaining a priest, the post-Conciliar Pontifical made one very slight change which silly people made a song and dance about. But the change in fact simply changed the wording back to what it had been in the first Christian millennium. If this wording really is inadequate to ordain, then S Gregory the Great, poor chap, went through his life ordaining invalidly. So did all the popes for more than a thousand years. People who claim this seem to me to be funny sorts of "Catholics".
I do get quite cross with these individuals who, because of their own passionate desire for "the Conciliar Church" not to have any true Sacraments, ignore what the Church has taught for centuries about validity.