"The extra-long leaders do often foul hook fish, many times hooked in the face or tail of the fish"

Seems to me that he is stating that the long leaders are legal but that fish hooked in the face or other places are considered foul hooked. I assume that it is not legal to keep foul hooked fish, so all fish not hooked in the mouth would be illegal. If it is legal to keep foul hooked fish, then the whole rules are screwed up.