if Jesus is Lord do you think He made a mistake transmitting the scripture to you?
if Jesus is Lord and Jesus promised to send the Holy Spirit why would you think it's 'wishful thinking' that men guided by that very promised Holy Spirit were able to discern the truth from the lie?
have a look at Acts 15. here is an example of humans coming together to determine the answer to hard questions, and being led by the Spirit to the correct conclusion. so you have a witness that it isn't impossible.
scripture testifies of Christ. John 5:39. there's one litmus test you can use.
in general as to non-canonical books, you may as well be asking why Bill O'Reilly's books aren't in the Bible.
because they're either devoid of Christ, of full of false teaching about Christ, is why.
why Bill's books are not there? You know you caused me to think something that was very interesting to me.
Bill "O" wrote the killing Book" of I think all those who he never met with the exception of JFK, and Ragan I think I could be wrong.
I know he did not meet Abraham lincoln or Crazy Horse. For bill O'Reilly books to be truthful HE had to have information of those he wrote about in the book who were:
1. eyewitnesses, or testimony from those who told what happens from an eyewitness. Just like a court of law out of the mouth of two or more witnesses.
2. other historical things to support the claim, landmarks, relics, archeological finds, etc..,.
The same is with the word of God we have EYE witnesses of the Lord Jesus Christ who saw his death and resurrection they died unwilling to deny that truth!
That is why the Bible is so powerful it is Truth! and God has kept it and HE always will. Many have tried to attack it, but it will stand forever.