Actually, I want to congratulate you on your excellent point. I think it is best to move the discussion to the canon of the 27 New Testament books because Protestants cannot defend with anything close to infallibility the canon of the N.T. The earliest list of those 27 books does not come up in extant texts until about AD 370.
The canon of the O.T. usually gets bogged down with secondary arguments over their worthiness.
After pointing to the necessity of the authority of the Catholic Church for the 27 New Testament books, then I will go to the secondary argument of O.T. and point out how the Bibles before Luther included the 7 Deuterocanonical Books.
defendingthebride.com/bb/judith.html
defendingthebride.com/bb/manuscripts.html
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