There are 25 Sundays between Trinity Sunday and Advent in the ORDINARIATE MISSAL ( O ... reproducing the texts of the 1662 Book of Common Prayer, which in turn derived them from the Sarum and other North European Uses). In the Tridentine Missal, they are 24. But in T, the first Collect of the series is assigned to Trinity Sunday itself, where it is used as a commemoration at the Mass of the Trinity and then in ferial masses during the week. In O, it is moved to the First Sunday after Trinity, which means that in effect the Trinity itself has an Octave (this disposition continues in CW, Common Worship); presumably, ferial masses in the following week are in white vestments. This also means that T is a Sunday ahead of O. But T also omits one of this ancient series of collects, the formula represented by O Trinity III (here is the original Latin of that prayer: Deprecationem nostram, qs, Dne, benignus exaudi: et quibus supplicandi praestas affectum, tribue defensionis auxilium). Because of this omission, for the rest of the year T is two Sundays ahead of O. (In what follows I shall exclude from consideration the Excita collect of the last Sunday before Advent, which, because of the imposition of Christ the King on this day, has its own problems).
CW restored, after the aberrations of the Alternative Service Book, the enumeration of the Sundays after Trinity (except that it terminates them before Advent so as to have a pre-Advent season concentrating on themes of the Kingdom and, optionally, in red vestments). CW also restores some of the old collects, and even allows them to occupy the same Sundays as in O. These collects are Trinity 1,4,6,7,10,11,12,19,21.
B (Bugnini) used some of the old series of collects; but, because of the invention of a novel 34-week tempus per annum, these survivors are all mixed up and only by very occasional coincidences will they fall upon their old Sundays. The collects thus preserved in B are the collects which, in O, are attached to the following Sundays after Trinity: 1,2,4,5,6,7,8,11,12,13,14,17,20. This is four more than CW. What I find interesting is that the taste of the CW committee and that of the B group did not always coincide. In six cases it did; but CW rather liked three which B despised; B liked seven which did not make the CW cut. (B did also incorporate into its new set a couple of collects which had originally lived After Easter but which were not 'paschal' enough in theme for the B peculiar eccentricity of treating all of the fifty days as the Easter Octave.)
The evidence supports the suspicion that these modern committee, in each communion, although working at around the same time and having many of the same presuppositions, did their picking and choosing and suppressing for the most part on the basis of pure personal whimsy, probably connected with which sides of their beds they had got out of.