True, the Mormons might be right in some of the appendages they add.
No false distinction. The writers of the New Testament were part of the Church but not part of the RC Church.
The RC Church is part of the Church but were not the writers of the New Testament.
I don't think that any writings were being added to accepted NT Scripture at that stage (450) so for all intents and purposes it was closed,,,,,,,,,,,,,,,,,,but no official authority had come up with an official statement to that end and sorted out which books it was going to accept and which it was not.
Not everyone agreed and not everyone agrees now.
Which accepted canon is correct do you think?
Personally I go with the same one the Jews went with for the OT and see the NT canon as those books written in the first century and having apostolic authority and association.
Only if you see the RC Church as being the Church and not just part of the Church.
Israel for example existed in the time of the Judges and before there was a Temple and sacrifices in the Temple and Kings etc.