The Protestant Old Testament is the same as the Hebrew Bible. These books are not in the Hebrew Bible. That's why Protestants don't have them. But all of the books he mentions are ancient Jewish works that are of considerable interest on their own terms. Wherever you put them, they should not be forgotten.
This doesn't even touch on the question of New Testament Apocrypha, some of which remained quite influential in Christianity into the Middle Ages. Professor Jenkins has dealt with that topic in detail too. See the links collected here. Also, related post here.
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