The additional three Eucharistic prayers were promulgated on 15 Aug 1968. Like other changes to the Order of Mass, these were printed in an insert by the bishop’s conference, which was intended to be glued into the altar missal, since the revised missal was nearing completion. (Why they didn’t just wait and include these in that is beyond me, but things were happening quickly.)
The revised Order of Mass was promulgated on 3 April 1969, and took effect on Advent Sunday, 1969. This was also printed in an insert, because the entire English missal was not published in the US until 1970. At the same time the new three-year lectionary was promulgated in a separate volume, and the revised Roman Calendar took effect on 30 Nocember 1969, when the missal and lectionary also began.
In some countries there were issues with the speed of the reforms and the ability to print and implement them. These places were given until 1971 to implement the entire missal.
The revised missal ran into some minor issues that needed tweaking, and a second edition (the one that most of us remember prior to the new translations a few years ago) was issued in 1973, and began to be used the following year.
This is lengthy (had to be split up into parts, due to length limitations), and probably contains typos that require correction, but I must go now. Ask questions as needed.