"Deuteronomy 12:32 “Whatever I command you, be careful
to observe it; you shall not add to it nor take away from
it.”
If I'm following your argument correctly, who had the
authority to add the other Scriptures after Deuteronomy?
The sealing of the book occurs in the last chapter:
Revelation 22:18-19 “For I testify to everyone who hears the words of the prophecy of this book: If anyone adds to these things, God will add to him the plagues that are written in this book; and if anyone takes away from the words of the book of this prophecy, God shall take away his part from the Book of Life, from the holy city, and from the things which are written in this book.”
My reading of the word is that all other commandments and laws following Deuteronomy came at the directive/inspiration from God and/or Jesus, not church and/or man, and were added to the book before it was sealed in Revelations.