I don't see it as a grey area. The law is actually very clear, in order to fly solo as the holder of a pilots licence, you must have a valid rating. If the rating has lapsed then you can't fly solo. In order to regain the rating you must undertake training as defined by the HoT of an ATO and take a skill test.
Certainly as a HoT myself, there is no way I would permit solo flight for a pilot training to regain a rating.