Yes, the Mass changed before 1969, repeatedly. Pretending otherwise would forfeit the argument, so we will not. The Last Gospel and other elements were universalized in the 1570 Missal; in 1884 Leo XIII added the Leonine Prayers after Low Mass; in 1911 Pius X reordered the psalter of the breviary in Divino Afflatu; in 1955 Pius XII restored the Holy Week rites; and in 1962 John XXIII inserted St. Joseph’s name into the Roman Canon, the first change to the Canon’s text in over a thousand years. The rite was never frozen, and the traditional case has never needed it to be.

But look at the character of those changes. A devotional prayer appended after Mass; a psalter redistributed; one saint’s name added; rites restored to a truer hour. Each was a limited, organic development (an addition, a restoration, a single insertion) that left the Order of Mass itself standing. None of them rewrote the structure of the rite. They are the pruning and grafting of a living tree, not the felling of it.

Be especially honest about 1955, because it is the strongest counter-example and traditionalists themselves debate it. Pius XII’s Holy Week reform was genuinely substantial, reshaping the most ancient ceremonies of the year, and some traditional Catholics prefer the pre-1955 books for exactly that reason. We grant all of that freely. It was a real, sizable reform. It was still nothing like the scope of what came in 1969.

Because 1969 was different in kind: a new Order of Mass, a rewritten Offertory, multiple new Eucharistic Prayers, a new lectionary and calendar. Even Paul VI named the scale of it (“a change in a venerable tradition… which seemed to enjoy the privilege of being untouchable.” So the honest claim is precise: yes, the Mass developed before 1969) organically, and in degree. What happened in 1969 was a change in kind.