Here is a section where John Chapman astutely discusses one of the proposed alternate translators for the Vulgate, Pelagius.
Journal of Theological Studies (1923)
John Chapman
https://books.google.com/books?id=snETAAAAIAAJ&pg=RA1-PA283
I am assuming already that St Jerome revised the whole New Testament. It is time to give the proofs. They are of overwhelming
strength.
The data are simple enough :
1. The ‘Vulgate’ New Testament is a revision of the whole New Testament—Gospels, Acts, St Paul, Catholic Epistles, Apocalypse—which has come down to us in an incomparably vast number of manuscripts. It was, in all these five portions, a revision of versions which existed before it in considerable variety. Its own varieties are due mainly to the infiltration of older readings. It is as definite a text as the Vulgate Old Testament.
....
Consequently, were it proved up to the hilt that Pelagius was all that he was not—a great textual scholar, a Hellenist, an explorer of manuscripts, a student of readings, a critic of Latin renderings—that his commentary’ (published before 410) was upon a pure Vulgate text—that Prologues, certainly by him, were prefixed to all Vulgate MSS of St Paul—one would still hesitate before admitting that the revision of the Apostle was due to him. For the question would arise : Who revised Acts? Who revised the Catholic Epistles? It would be difficult enough to have accepted Pelagius and St Jerome as authors each of a part. But that three or more authors, working on the same lines, with the same methods, revising according to the same type of Greek MSS, should have produced three or more homogeneous revisions of three or more divisions of the New Testament, and that these three ot more portions should have become the homogeneous whole which we know, and should have come down to us in one great tradition—this would be so improbable
a priori, that one would have been inclined to put aside the most convincing proofs about Pelagius until something could be discovered as to the reviser of Acts and the rest, and some hypothesis (at least) could be suggested to account for the union of the parts in one dominant whole, which conquered and utterly destroyed all pre-existing versions.
But Pelagius is fortunately out of the question. There is no other claimant for St Paul; there is no claimant at all for the other portions, —except, of course, St Jerome.
It is admitted that the Gospels are by St Jerome. We are perfectly free to attribute the whole of the homogeneous revision to the same reviser. It is the obvious thing to do. I believe I have removed the only objections that could be raised.
5. Tradition is unanimous. Until the few rather hasty modem critics, not a voice was ever raised to suggest that St Jerome did not revise the whole New Testament. The victorious career of the Vulgate is entirely due to the fact that it was universally believed in early times to be a revision carried out by the most learned of Western Doctors at the bidding of Pope Damasus. It is true that the Old Latin did not immediately expire, and that St Gregory the Great at the very end of the sixth century declared that the Roman Church used the old version as well as the new. In theory, yes. But even from St Jerome’s time onwards, pure Old Latin is not often to be found for the N. T. We have Vulgate, impure Vulgate, and mixed Old Latin and Vulgate, but no longer a rival Old Latin. The Vulgate triumphs early, and eventually triumphs completely.
6. And behind this tradition we have absolutely definite and categorical statements by St Jerome himself, that he revised the whole New
'Testament.
p. 282-285