That’s a subject that Fr. Jungmann took two large volumes to discuss, and Cardinal Schuster spent eight volumes on. But I’ll try to encapsulate it for the Latin or Roman Rite.
The EF as we knew it just before and after Vatican II was a modification of the Missal imposed on any Latin Rite diocese, or Religious Order that did not have a Rite of the Mass which was 200 years of age and in constant used prior to the publication of his Missal.
Prior to the “Pian” Missal, Mass was celebrated in similar but varied manners around western Europe. Different reading were appointed in different areas, The Ambrosian Rite, which was used in the area around Milan had different prayers, as similar Canon to the Roman Canon, and earlier missals had far more prefaces before the Canon. But let’s stick to the Roman Rite.
Before the Council of Trent, and the Pian Missal, the prayers at the foot of the altar were a private devotion of the priest, recited by the priest and the server or sacred ministers on the way to the altar. The Last Gospel was also recited by the priest as he left the altar and was not part of the Mass itself. One knew the priest was not an Aryan if he genuflected at the Et Verbum Caro Factum Est. There were many feasts that had proper last Gospels, whereas today there are only a couple of times a year that the Last Gospel is not the First chapter of St. John. In the Canon, local saints, were invoked, and after the Commemoration of the Pope and Bishop the Holy Roman Emperor and local King was commemorated. This remained for a time after the Council of Trent, so for those in the Sede Communities who say that the Canon cannot be changed, I guess they have to scribble in the commemoration of the Holy Roman Emperor and King, even if the priest omits it since we don’t have them in the USA.
As for the Kyrie, in the EF we have three Kyrie, three Christie, and three Kyrie, harkening to a petition to the Trinity. But these were simply a minimal retention of the practice of reciting long litanies as the priest would sprinkle holy water, incense the entire church and preform other rites to prepare for the Sacrifice. Anyone who has been to the Byzantine Rite and heard the beautiful litanies, with the Lord have mercy, in the liturgy can see the similarity. You may want to look at a Byzantine Catholic liturgy on Youtube to see what I’m referring to. In many places the readings from the sacred scriptures were like the OF from OT, Epistle or Apocalypse and then Gospel. In the early Church the reading went as long as the bishop or priest wanted it to, and he would signal when enough had been read.
While in the earliest liturgy the canon, or Eucharistic prayer was composed by the individual Bishop, based on what the Apostle who ordained him had instructed, as the Church grew the Canon became fixed so bishops and priests would offer the sacrifice in a manner that was similar. Eventually local councils fixed the canon in each area.
The earliest liturgies were split between the prayers and hymns then readings, after which a sermon was preached instructing the people. After that the catechumens and anyone who was preforming a penance would be dismissed then the offering of the bread and wine consecration and communion would take place. Some people were imposed penances that could last from months to years, and would be required to attend the Liturgy of the Catechumens and not be allowed to receive communion or assist at the Liturgy of the Faithful until their penance was completed. So from the Creed to the last blessing if you had committed a sin, confessed, and been absolved you still had to preform a strict penance before you were readmitted to communion.
As I think of other things, and review Fr. Jungmann, I’ll add some more, probably in a new thread.