Conclusion.*
30
Now Jesus did many other signs in the presence of [his] disciples that are not written in this book.
31
But these are written that you may [come to] believe that Jesus is the Messiah, the Son of God, and that through this belief you may have life in his name.t
You’re right.....this indicates Holy Tradition. That many truths were passed down face to face, person to person and they aren’t necessarily recorded in the Bible.