Note the argument in Adv Haer 3.10 - 11. Irenaeus originally makes the argument that:
This, therefore, having been clearly demonstrated here (and it shall yet be so still more clearly), that neither the prophets, nor the apostles, nor the Lord Christ in His own person, did acknowledge any other Lord or God, but the God and Lord supreme: the prophets and the apostles confessing the Father and the Son; but naming no other as God, and confessing no other as Lord: and the Lord Himself handing down to His disciples, that He, the Father, is the only God and Lord, who alone is God and ruler of all; -- it is incumbent on us to follow, if we are their disciples indeed, their testimonies to this effect.
His next task is to go through each gospel and show that at the beginning of each gospel each author uses the Jewish scriptures which Irenaeus believes are rooted in monotheism. So in the very next line he writes:
For Matthew the apostle -- knowing, as one and the same God, Him who had given promise to Abraham ...
He then proceeds to discuss the beginning of Matthew and its use of an angel from the Jewish god then the beginning of Luke (oddly) and its reference of an angel from the Jewish god and then proceeds to discuss the beginning of Mark:
Wherefore also Mark, the interpreter and follower of Peter, does thus commence his Gospel narrative: "The beginning of the Gospel of Jesus Christ, the Son of God; as it is written in the prophets, Behold, I send My messenger before Thy face, which shall prepare Thy way. The voice of one crying in the wilderness, Prepare ye the way of the Lord, make the paths straight before our God." Plainly does the commencement of the Gospel quote the words of the holy prophets, and point out Him at once, whom they confessed as God and Lord; Him, the Father of our Lord Jesus Christ, who had also made promise to Him, that He would send His messenger before His face
In each of the previous sections dealing with Matthew and Luke the emphasis is on the appearances of angels who come from the Jewish god. One would expect that the argument here would be that Mark too is speaking about the coming of an angel of the Jewish god but the text suddenly changes and a later editor likely adds the following:
... who was John, crying in the wilderness, in "the spirit and power of Elias,"(1)"Prepare ye the way of me Lord, make straight paths before our God." For the prophets did not announce one and mother God, but one and the same; under rations aspects, however, and many titles. For varied and rich in attribute is the Father, as I have already shown in the book preceding this; and I shall show [the same truth] from the prophets themselves in the further course of this work.
Indeed in order to correct the change (i.e. the introduction of John the Baptist in a later version of Mark) the author is forced to go to the end of the gospel and the longer ending (which again was added by Irenaeus most certainly):
Also, towards the conclusion of his Gospel, Mark says: "So then, after the Lord Jesus had spoken to them, He was received up into heaven, and sitteth on the right hand of God; "(3) confirming what had been spoken by the prophet: "The LORD said to my Lord, Sit Thou on My right hand, until I make Thy foes Thy footstool."(4) Thus God and the Father are truly one and the same; He who was announced by the prophets, and handed down by the true Gospel; whom we Christians worship and love with the whole heart, as the Maker of heaven and earth, and of all things therein.
We know that the original argument of Irenaeus was that all the 'starts' to the gospel make reference to an angel who belonged to the Creator because immediately following the discussion of the beginning of Matthew, Luke and Mark he goes on to discuss the angel - the Word - at the beginning of John:
John, the disciple of the Lord, preaches this faith, and seeks, by the proclamation of the Gospel, to remove that error which by Cerinthus had been disseminated among men, and a long time previously by those termed Nicolaitans, who are an offset of that "knowledge" falsely so called, that he might confound them, and persuade them that there is but one God, who made all things by His Word; and not, as they allege, that the Creator was one, but the Father of the Lord another; and that the Son of the Creator was, forsooth, one, but the Christ from above another, who also continued impossible, descending upon Jesus, the Son of the Creator, and flew back again into His Pleroma; and that Monogenes was the beginning, but Logos was the true son of Monogenes; and that this creation to which we belong was not made by the primary God, but by some power lying far below Him, and shut off from communion with the things invisible and ineffable. The disciple of the Lord therefore desiring to put an end to all such doctrines, and to establish the rule of truth in the Church, that there is one Almighty God, who made all things by His Word, both visible and invisible; showing at the same time, that by the Word, through whom God made the creation, He also bestowed salvation on the men included in the creation; thus commenced His teaching in the Gospel: "In the beginning was the Word, and the Word was with God, and the WOrd was God. The same was in the beginning with God. All things were made by Him, and without Him was nothing made.(5) What was made was life in Him, and the life was the light of men. And the light shineth in darkness, and the darkness comprehended it not."(6) "All things," he says, "were made by Him;" therefore in "all things" this creation of ours is [included], for we cannot concede to these men that [the words] "all things" are spoken in reference to those within their Pleroma. For if their Pleroma do indeed contain these, this creation, as being such, is not outside, as I have demonstrated in the preceding book;(7) but if they are outside the Pleroma, which indeed appeared impossible, it follows, in that case, that their Pleroma cannot be "all things:" therefore this vast creation is not outside [the Pleroma].
2. John, however, does himself put this matter beyond all controversy on our part, when he says, "He was in this world, and the world was made by Him, and the world knew Him not. He came unto His own [things], and His own [people] received Him not."(8) But according to Marcion, and those like him, neither was the world made by Him; nor did He come to His own things, but to those of another. And, according to certain of the Gnostics, this world was made by angels, and not by the Word of God. But according to the followers of Valentinus, the world was not made by Him, but by the Demiurge. For he (Soter) caused such similitudes to be made, after the pattern of things above, as they allege; but the Demiurge accomplished the work of creation. For they say that he, the Lord and Creator of the plan of creation, by whom they hold that this world was made, was produced from the Mother; while the Gospel affirms plainly, that by the Word, which was in the beginning with God, all things were made, which Word, he says, "was made flesh, and dwelt among us."(9)
3. But, according to these men, neither was the Word made flesh, nor Christ, nor the Saviour (Soter), who was produced from [the joint contributions of] all [the Aeons]. For they will have it, that the Word and Christ never came into this world; that the Saviour, too, never became incarnate, nor suffered, but that He descended like a dove upon the dispensational Jesus; and that, as soon as He had declared the unknown Father, He did again ascend into the Pleroma. Some, however, make the assertion, that this dispensational Jesus did become incarnate, and suffered, whom they represent as having passed through Mary just as water through a tube; but others allege him to be the Son of the Demiurge, upon whom the dispensational Jesus descended; while others, again, say that Jesus was born from Joseph and Mary, and that the Christ from above descended upon him, being without flesh, and impassible. But according to the opinion of no one of the heretics was the Word of God made flesh. For if any one carefully examines the systems of them all, he will find that the Word of God is brought in by all of them as not having become incarnate (sine carne) and impassible, as is also the Christ from above. Others consider Him to have been manifested as a transfigured man; but they maintain Him to have been neither born nor to have become incarnate; whilst others [hold] that He did not assume a human form at all, but that, as a dove, He did descend upon that Jesus who was born from Mary. Therefore the Lord's disciple, pointing them all out as false witnesses, says, "And the Word was made flesh, and dwelt among us."
The point again is that the development of the canonical gospels was gradual. Irenaeus makes reference to things in Mark which now no longer appear in Mark. One may imagine a twenty or thirty year period for the gestation of the texts as we have them and that variety to be reflected in the surviving commentaries or fragments of older commentaries.
“Finally, from so little sleeping and so much reading, his brain dried up and he went completely out of his mind.”
― Miguel de Cervantes Saavedra, Don Quixote