As liturgical geeks like me know, the ancient vigil of Pentecost was brutally slaughtered in the 1955 Holy Week reform. The end of the decree simply suppresses it altogether, save the Mass part of it. This, like so many of the 1955 reforms, left the prayers and words said incomprehensible and at times false. See there was also a special vigil of Pentecost, in many ways like the pre1955 Easter Vigil, and baptisms were also done then (which is why Pentecost is often called Whitsunday in older texts, or White Sunday, from the white of the neophytes). Of course Pentecost also had an octave.

Well lo and behold, while everyone focused on the change in translation, something many people missed was that the translation was of a different missal. The old translation was that of the "2nd Edition" of the Roman Missal (which came out only a few years after the first edition of the Novus, probably in large part because in 1973 Paul VI abolished the minor orders and the subdiaconate, neccessitating further changes in the Mass). The new translation if of the 2002 Missale Romanum

So why a new edition? Because there were changes to the Latin Missal itself. One of those changes was the unanticipated restoration (at least partial) of the Vigil of Pentecost. It is optional and called the "longer form" See originally Easter Vigil, Ember Saturdays and Pentecost vigil had 12 readins, these were cut to 6 in the 6th century, but Holy Saturday gradually gained back the other 6 prophecies making 12 [until 1955]. In 1955 all 6 were abolished in the Vigil of Pentecost.

I am not 100% sure what exactly was restored (I lack a 2002 MR right now), so I am curious if anyone knows exactly

I don't know, but last year we did a full blown Pentecost vigil in the ordinary form at our parish. I know it was an option even then.

ETA: That said, I remember we had to do a heck of a lot of digging to figure out the right readings and Psalms and so on. I ended up composing parts of the Psalm settings.