That's what I've always thought; too.
I wonder...
Could there be a yet unfound FOURTH letter from John; telling of all the wondrous things that Mary had been doing for the Kingdom while she lived with him?
I always wondered, too, about the fact that Jesus personally taught the Apostles for 40 days between His Resurrection and His Ascension, and none of it is recorded.
Maybe that is why the Scriptures command us to cling not only to the written words, but to the Tradition --- what was handed down via the Apostles' disciples, whether by word or by example.
One chain of transmission:
John --> Polycarp of Smyna--> Irenaeus of Lyon.
We know the content of this Oral Tradition because within a generation or two it was written: we have the writings of the men the Apostles taught, and we know of the practice of their churches: their liturgy and so forth.
Hence the Church's axiom ,"Lex orandi, lex credendi." The way they prayed is what they believed.