I have always wondered about this.
The quotes are not really quotes... they do not say "from the gospel xxx" or anything like that.
Actually many of them do:
First of all, after He had made the water wine at Cana of Galilee, He went up to the festival day of the passover, on which occasion it is written,
"For many believed in Him, when they saw the signs which He did",
as John the disciple of the Lord records. -
Against Heresies (Book II, Chapter 22)
Given the way things are translated the hilighted passage fits John 2:23 very well.
Just a little further
For when He came to be baptized, He had not yet completed His thirtieth year, but was beginning to be about thirty years of age (for
thus Luke, who has mentioned His years, has expressed it:
Now Jesus was, as it were, beginning to be thirty years old, when He came to receive baptism);...
A good summation of Luke 3:21-23
Against Heresies (Book III, Chapter 11) talks about the four Gospels we have:
For the Ebionites, who use
Matthew's Gospel only, are confuted out of this very same, making false suppositions with regard to the Lord. But Marcion,
mutilating that according to Luke, is proved to be a blasphemer of the only existing God, from those [passages] which he still retains. Those, again, who separate Jesus from Christ, alleging that Christ remained impassible, but that it was Jesus who suffered, preferring the
Gospel by Mark, if they read it with a love of truth, may have their errors rectified. Those, moreover, who follow Valentinus,
making copious use of that according to John, to illustrate their conjunctions, shall be proved to be totally in error by means of this very Gospel, as I have shown in the first book.
They are at best a phrase that RESEMBLES something in the gospels which then "scholars" construe as a quote in the most tortured sense.
Actually this may be is a translation and coping issue. We know that even the canonal four had their variants.
But has anyone questioned that this phrase could have been something floating around and the gospel writers borrowed it as they did almost everything else?
Again we KNOW there were more then four Gospels even in the late 2nd century as not only does Irenaeus wrote about them but Egerton Papyrus 2 range mid point (175 CE) is the correct time for when
Against Heresies was supposedly composed.
If Irenaeus was paraphrasing stuff that was already bouncing around then why not just saying it was corrupted and the four Gospels he was on about actually said something else? It seems more likely per Occam's Razor that Irenaeus was using already existing works that he paraquoted from then him dreaming up passages that were later incorporated into the Gospels we know.
Also Irenaeus claim in Demonstrations ("For
Herod the king of the Jews and Pontius Pilate, the governor of
Claudius Caesar, came together and condemned Him to be crucified") shows that he HAD to be working off of existing documents. If Luke didn't exist at that time then Irenaeus would not have been locked into putting Jesus' crucifixion in the time of Claudius Caesar by his Jesus having the age of a Teacher (46+ years old) position as he was and then shoe horning Pontius Pilate into that time period as he did.
A 34 year old Jesus in 28 CE
would be 50 years old in 44 CE which is the last year Herod "King of the Jews" (i.e. Herod Agrippa I) ruled.
The fact in places like Book II, Chapter 22 where he nearly bends over backwards to get things to fit his own views shows the group he was part of has their own "set" canon and that likely means written works.