In an earlier post I pointed to some striking parallels between the Vulgate edition of the pericope adulterae (= PA) and the circumstances of Jerome’s expulsion from Rome, apparently under accusations of sexual impropriety. Considering various anomalies in Jerome’s testimony concerning the PA, I raised the question as to whether Jerome himself may have contributed to its final form.
I had already drafted the above post when last Saturday I attended Amy M. Donaldson’s paper, “‘What Was Spoken through the Prophet Asaph’ (Matt. 13:35): Textual Evidence from Jerome, or Conjectural Emendation by Origen?”, at the Pacific Northwest Regional SBL meeting on the variant “through Asaph” (ασαφ) in Matthew 13:35.  Since the reading lacks any surviving continuous manuscript support, the external evidence rests entirely on Jerome’s remarks. 
Fortunately, since Jerome comments on the reading on two separate occasions, we are able to compare his respective accounts and assess his reliability. In fact, the results are not favorable to Jerome’s credibility. When he first mentions the reading in his Commentary on Matthew (398), it is still conjecture :
I have read in several manuscripts [Legi in nonnullis codicibus], … that … it is written as ‘through Isaiah the prophet, saying.’ Because the text is not at all found in Isaiah, I think it was later removed by prudent men. In my judgment [Sed mihi uidetur], it was originally published as follows: ‘[in order that what was written] through Asaph the prophet, saying.’ (Comm. Matt 13:35). 
Yet just a few years later, in his Homily 11 on Psalm 78 (77 LXX) (401), Jerome confidently asserts that what had formerly been in his judgment “is found in all the ancient copies” (in omnibus ueteribus codicibus).  It is unlikely of course that Jerome had discovered any actual MSS in the few years between these remarks. Presumably he would have mentioned such favorable evidence! So we are forced to ask, is Jerome extrapolating on the basis of a self-assured conjecture to evidence that he simply never saw? 
Whatever his motives, Jerome’s lack of inhibition in ascribing his personal conjecture to the Greek MS tradition should give us pause in assessing the reliability of his remarks elsewhere. Imagine that Homily 11 had been our only surviving source for the reading ασαφ in Matthew 13:35. We would quite reasonably infer that, had Jerome found this reading in all of his copies, it must have been at least in a great number of Greek copies. Yet we would be utterly mistaken!
Fast-forwarding to the year 415, Jerome asserts that there then existed “many Greek and many Latin codices” with the PA (Pelag. 2.17). But surely Jerome is being somewhat disingenuous in his appeal to “many” Latin copies. After all, this figure included copies of the Vulgate that he had himself revised to include the PA! And why is it necessary to cite Latin evidence at all for a reading that exists in many Greek MSS? Are we to wonder then whether Jerome is extrapolating in this case also to Greek evidence he never saw?
 University of Idaho, May 21, 2016.
 The evidence is still cited in NA28 and (apparently) UBS5. Jerome’s starting point seems to be Origen’s conjecture.
 Date according to Gryson et al., Répertoire général des auteurs ecclésiastiques latins de l’antiquité et du haut Moyen Âge (2007) 1:540.
 Cited from Dr. Donaldson’s handout, which cites FC 117:160-161; SC 242:284.
 Date according to Gryson et al., 1:545. Cited from Dr. Donaldson’s handout, which cites FC 48:81-82 in modified form and CCSL 78:66-67.
 Dr. Donaldson plausibly suggests that Jerome simply assumed that his inference was correct and hence present in the old copies. See also, Amy M. Donaldson, “Explicit References to New Testament Variant Readings among Greek and Latin and Church Fathers.” (PhD Diss.; University of Notre Dame, 2009) 369-372, where she observes, “The homilist therefore assumes that Asaph is the predominant and oldest reading.” (p. 370) “Jerome especially emphasizes that his conjectured original reading, Asaph, is theologically correct …” (p. 372)