The gospels were written along time after Jesus died, I don't see how it is possible for even those who knew Jesus in person to have been able to quote him word for word years later. I very much doubt they wrote them down at the time he was actually supposed to have said those things. What Jesus actually said and the meaning of his words, could have been very different to what the gospels quoted him as saying.
How many of us could quote accurately word for word something which was said to us last week, for instance? The game of Chinese whispers makes my point well, a sentence which is passed down the line is nothing like it was when it started out.
I first walked into the church where I still worship on the first Sunday of September 1969, some 48 years ago. I seem to recollect that it was Sunday 7th. The subject of the sermon was a look at earthquakes found in the Scriptures and what we could learn and apply from them. I can still remember quite a bit of the detail. The minister moved to another church at the end of 1975 and I also have very clear recollections of aspects of many other of his sermons during this period. These included messages on the young man in the tomb in Mark's Gospel, the healing of Jairus' daughter, the calming of the storm on Galilee and the Letter to the Church at Ephesus in Rev 2. In September 1975 the minister whom we were considering as a potential replacement was invited to spend a few days at the church and on the Sunday he preached on the text from Genesis 50:20, 'you meant it for evil but God meant it for good'. I can remember much of that sermon too.
In fact in the 1990's I preached a sermon on the Letter to the Church at Ephesus' which was little more that a direct plagiarising of what I could remember of the sermon I heard early in the 1970's. I was surprised at how much more came to mind as I prepared.
So while I have forgotten much of what was said in the sermons I heard well over 40 years ago, I can confidently say that what I remember is correct and, if I committed them to paper (as I did the Ephesus sermon), what I did write would be accurate and a true reflection of the original teachings.
How much more detail would I still have if I had been asked to share on a regular basis my recollections of what these two men preached had I been requested to do so on a regular basis from the time immediately following their moves to other churches?
So I have no problem with the accuracy of the NT writings given a time of writing some 40-50 years after the event.
Needless to say that I am of the view that the great majority of the NT documents were written well within that time frame with only the 4th gospel being a bit later.