St. Jerome did not exercise any personal judgement when he translated the Old Testament Vulgate: he simply translated the Septuagint, which included the Deuterocanonical books.
The canon was well established prior to Jerome's work, albeit not formally till early 400 at Carthage. The crieteria for inclusion were verifiability of source, a link to the apostles, and doctrinal solidity of content. Works that would be useful but did not directly relate to the deposit of faith left by Christ were not included, no matter how convenient politically it would have been to include them. For example, there was a lot of consideration done to the letter of Clement to Corinthians: it served the papacy well and contained much theological teaching, and was quite early. But Clement was no apostle, and so the letter was secondary in its theology. It was not included.
what they claim in there could hardly be relied upon by a historian
Some of the apocryphal Acts I read, and some contain accounts that a modern reader would see as fantastic. However, they are still evidence inasmuch as they also refer to hard facts. We are religion of miracles and a church of miracles. It makes little sense, for example, to discard a biography of an apostle (forget which one) as a whole because it contains the unlikely story how that apostle first baptized a lion, and then encountered the same lion in the circus.