Those gospels that didn't make the cut would appear to be at 4:21 the Gnostic Gospels. (I'd include a screen shot if I knew how to do it.)
They didn't make the cut for the very good reason that they were known to not be of Apostolic Origin. The Gospel of Thomas for instance was written about 150AD and clearly after the death of all those who knew Jesus. While it includes many authentic sayings it also includes fake sayings to promote gnosticism.
Actually Luke refers to "Many have undertaken to draw up an account of the things that have been fulfilled among us" which suggests there were other accounts even during the lifetimes of the Apostles. The four canonical gospels were accepted by the church because those who knew Jesus were alive to verify their accuracy.
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