I agree, this appears to be an omission. The diagram between 17a and 17b implies that the neighbouring areas are not in play at all, so are effectively Allied-friendly (i.e. can't support a counterattack). The setup for a 2-player game supports this supposition.
Please treat them in a solo game as Allied friendly if you want to play on a level easy. If you want to play on a level hard, treat them as open roads for the possible counterattacks.