Since the 1570 Missal of Pius V was issued in the wake of the Council of Trent, the ancient rite has often been referred to as the Tridentine Mass. While there is nothing inherently wrong with this term, it can (and has) been used by some seeking to diminish the ancient rite by implying that it only dates back to 1570.
This, of course, is a myth.
Writing 50 years before the Second Vatican Council (1962-1965) and the promulgation of the new Mass of Paul VI (1970), Father Adrian Fortescue discussed the very antiquity of the Roman Rite in his classic, The Mass: A Study of the Roman Liturgy (1912):
“Essentially the Missal of St. Pius V is the Gregorian Sacramentary; that again is formed from the Gelasian book which depends on the Leonine collection. We find the prayers of our Canon in the treatise de Sacramentisand allusions to it in the IV century. So our Mass goes back, without essential change, to the age when it first developed out of the oldest liturgy of all. It is still redolent of that liturgy, of the days when Caesar ruled the world and thought he could stamp out the faith of Christ, when our fathers met together before dawn and sang a hymn to Christ as to a God. The final result of our enquiry is that, in spite of unsolved problems, in spite of later changes, there is not in Christendom another rite so venerable as ours.”
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I assumed TLM and Tridentine are the same. If not my apologies. I certainly did not mean to denigrate it. I’m not honestly sure how old TLM is. You state a general misconception of about 450 years, I thought 800. When did this form of the mass start being used? There are many Liturgies that date back to the first 4 centuries, I don’t believe this is one of them. I would be happy if you could further enlighten me.