This existence of local development and variations between missals prior to their mass production by the printing press should not be source of scandal. I dear say that the situation in the Byzantine Rite at the time was similar. It should be remembered that the Great Entrance, that hallmark of the Byzantine liturgy, did not become current in Constantinople until the 6th/7th century. Even today there are differences in usages between the Greeks, Serbs, Russians, etc.
I think it would be fair to say that I denied the extent of antiquity of the traditional Mass, to which the history of Mass leads us. But I was definitely wrong in believing that the traditional Mass was of a much more recent origin. All indications are that the Roman Rite Mass has been set canonically for all practical purposes by the 7th century, which represents a "pedigree" of 14 centuries vs 16; insignificant difference indeed.
It should be remembered that the Great Entrance, that hallmark of the Byzantine liturgy, did not become current in Constantinople until the 6th/7th century
No doubt, things have been added and changed in all liturgical forms; the essential point is to establish at what point a Divine Liturgy/Mass would be recognizable and familiar to present-day laity.
In the case of Eastern liturgies, clearly the one of +John Chrysostom and +Basil (going back to late 4th and early 5th centuries) would be, despite minor changes, as they are served to this day on a regular basis (the latter about a dozen times a year).
The Divine Liturgy of St. James (the Just) contains many of the elements of the DLs of +Basil and +Chrysostom, but is obviously not the same liturgy (which also contains many OT references and prayers).
According to the New Advent Catholic Encyclopedia, the clear line between the Mass as is known today is seen with Pope +Gregory I and why:
"We come now to the end of a period at the reign of St. Gregory (590-604). Gregory knew the Mass practically as we still have it. There have been additions and changes since his time, but none to compare with the complete recasting of the Canon that took place before him...
"We may say safely that a modern Latin Catholic who could be carried back to Rome in the early seventh century would – while missing some features to which he is accustomed – find himself on the whole quite at home with the service he saw there."
The Great Entrance is a modification of the praxis of earlier days when the Gifts were prepared outside the church and were brought in to the altar. Today, they are prepared on a separate table near the altar and the priest walks them around the church simulating their being brought in.
The hallmark is the appearance of the Gifts, not the manner in which they are presented to the congregation.
But I am surprised you mention the Great Entrance modification and neglect to note the true Byzantine innovation of mixing the Body with the Blood in the Cup and distributing it via a small golden spoon for Holy Communion!
Even today there are differences in usages between the Greeks, Serbs, Russians, etc
Yes, of course. One very obvious difference is that Slavonic Divine Liturgies have Beatitudes in the Third Antiphon and the Greek doesn't. There are external variations as well, but none of these are canonical.
My objection to the 1,600-year-old antiquity of the traditional Latin Mass was off. I was under the wrong impression that it was of a more recent origin and, while I guess it would be easy to blame liberal Catholics for creating this impression, I will just blame my ignorance and be contant to confess my error.
It is clear that the traditional Latin Mass has been in use for about 1,400 years. It is equally clear that two centuries prior to that include significant canonical changes as the Mass evolved from being essentially Eastern and not something modern-day Catholics could be "quite at home with," into a Western form that is canonically unchanged until today.