the Deut 18 scriptures in question are from verse 18 onwards although you can look at the whole chapter for context. What you are doing is proof texting and taking them out of context.
18 I will raise up for them a prophet like you from among their brothers; I will put my words in his mouth, and he will tell them everything I command him. 19 If anyone does not listen to my words that the prophet speaks in my name, I myself will call him to account. 20 But a prophet who presumes to speak in my name anything I have not commanded him to say, or a prophet who speaks in the name of other gods, must be put to death."
21 You may say to yourselves, "How can we know when a message has not been spoken by the LORD ?" 22 If what a prophet proclaims in the name of Jehovah does not take place or come true, that is a message Jehovah has not spoken. That prophet has spoken presumptuously. Do not be afraid of him.
The context for all these scriptures is when God speaks words to the prophets directly. This is the creteria for inspiration in the bible so they knew which books were inspired or what was prophetic utterances. Hense why the Bible is called "God's word".
These scriptures are also pointing towards the messiah and how to recognise him.
Unless someone is claiming to be specifically inspired of God, actually able to hear God's words directly these scriptures do not apply. Witnesses have never claimed inspiration and have actively denied it.
The Bible already shows Nathan and the apostles making mistakes among others and not getting called false prophets for it. So I don't have to prove anything the Bible has already proved it for me.
Wasblind you are just putting impossible creteria on mankind by your reasonings which do not allow for refinement from God's word itself.