I will say this though: most of the tests that can add wound modifiers actually state that you subtract the wound modifiers from the test. That's not the case with either of the natural healing tests. So I'd say that wound modifiers do apply, but I'd be totally comfortable with this not being true. Since the rules came from different sections, it's possible (even likely) that the contradiction was unintentional. Perhaps there was an omission of text in the rule that I cited.