The early churches did not decide on anything other than the AUTHENTICITY of the writer. Once they established that a writing had apostolic authority, they accepted it as binding on them.
It would be like your receiving a note that seemed to be from your boss. Once you were able to determine that it actually DID come from your boss, then you would take it seriously. If you found out that it did not come from your boss, then you would not take it seriously.
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There are writings by the same people who had apostolic authority that have been authenticated since the cannon of the bible was set.
Should these writings be added to the bible?
No, there are not.
There are no other writings with the verified stamp of the Apostolic eyewitnesses of the resurrection.
Name even one, and quick study will easily demonstrate that you are wrong.
Trust me, if there were another known, verified book of the Apostle Peter or John just lying around in a bookcase, it would be part of the Bible.