My lovely wife helpfully posted this Gerhard quote on the perfection of Scripture:
"we are not calling Scripture "perfect" in this sense that all the things necessary for faith and behavior are present in Scripture literally and in just so many words. Rather we are saying that Scripture contains some matters explicitly and some implicitly so that we can deduce from Scripture the legitimate and immovable consequence. The fact, therefore, that Bellarmine in the passage we soon are going to cite, and the Jesuit Bailius, catech., treatise 1, q.10, deny that Scripture contains all things expressly which are necessary for salvation; I say, that fact we concede if we take that as meaning the sound of the words; but if the mean the truthfulness of the matter, we deny it. We say with Nazianzen, orat.5, de theol.: "There are some matters which, although Scripture may not say then word by word and expressly, we nevertheless conclude from them that they necessarily cause and prove that.""