Technically the bolded statement is correct - at least for the first dog. I wonder if this is not a question of letter vs. intent. There are no marks down when the dog is sent for the blind, but there sure is a lot of scent out there on both sides whereas it is usually only on one side. So while the rules as written don't seem to disallow the up-the-middle blind, I wonder if this is what was intended.
Of course, the simple answer is to train for up-the-middle blinds. Remind me I said that.