On the whole, Irenaeus seems to have had a pretty complete knowledge of the writings and teaching of the Valentinians.

We conclude therefore, that, while it cannot be alleged positively that any of the quotations or allusions were really made by Valentinus, it would be rash to assert that none of them were made by him, or that he did not use our present Gospels.
However this may be, we cannot do otherwise than demur to the statement implied in 'Supernatural Religion' [Endnote 198:1], that the references in Irenaeus can only be employed as evidence for the Gnostic usage between the years 185-195 A.D.This is a specimen of a kind of position that is frequently taken up by critics upon that side, and that I cannot but think quite unreasonable and uncritical.

Without going into the question of the date at which Irenaeus wrote at present, and assuming with the author of 'Supernatural Religion' that his first three books were published before the death of Eleutherus in A.D.

190--the latest date possible for them,--it will be seen that the Gnostic teaching to which Irenaeus refers is supposed to begin at a time when his first book may very well have been concluded, and to end actually five years later than the latest date at which this portion of the work can have been published! Not only does the author allow no time at all for Irenaeus to compose his own work, not only does he allow none for him to become acquainted with the Gnostic doctrines, and for those doctrines themselves to become consolidated and expressed in writing, but he goes so far as to make Irenaeus testify to a state of things five years at least, and very probably ten, in advance of the time at which he was himself writing! No doubt there is an oversight somewhere, but this is the kind of oversight that ought not to be made.
This, however, is an extreme instance of the fault to which I was alluding--the tendency in the negative school to allow no time or very little for processes that in the natural course of things must certainly have required a more or less considerable interval.
On a moderate computation, the indirect testimony of Irenaeus may be taken to refer--not to the period 185-195 A.D., which is out of the question--but to that from 160-180 A.D.This is not pressing the possibility, real as it is, that Valentinus himself, who flourished from 140-160 A.D., may have been included.

We may agree with the author of 'Supernatural Religion' that Irenaeus probably made the personal acquaintance of the Valentinian leaders, and obtained copies of their books, during his well-known visit to Rome in 178 A.D.