The Gospel of John may be the first Gospel that we know of to bring the question of its author’s credentials into the work itself (the Gospel of Luke does something similar, with its emphasis on the author’s research, but it may or may not be earlier than John).
In the period not long after this, we would see a proliferation of Gospels, letters, and other works appealing to named apostles in order to vouchsafe the new ideas that they were introducing.
The author/editor of the Gospel of John very cleverly puts no specific name to the source that is supposed to vouchsafe its reliability, making it impossible for anyone to contradict him. (This issue would not exist in a slightly later period, when living people with connections to members of the first generation of Christians were few and far between, if not already deceased). But other than that, the Gospel of John fits the pattern we find in later times: it introduces radically new ideas, and offers an eyewitness who allegedly knew Jesus as guarantor of this teaching.
What should we make of this? Should the Gospel of John be seen as the last recollection of an eyewitness, filtered through age and editing, as some claim? Or should it be seen rather as a first step in the direction of appealing to apostles and eyewitnesses to introduce new innovations, in an attempt to get them accepted?
What do readers think? I admit to having gone back and forth on this, and even wonder sometimes if there may not be a bit of both, i.e. some actual historical recollections independent of the other Gospels, eventually embedded in a text which also introduces significant innovations, which its author seeks to support through an allusive appeal to authority.