The first solo nav is exactly that... a first SOLO nav. Presumably a number of dual Nav's took place prior.
Where does it end though? You can't just not send a student on a nav because there may be cloud in the area.
I'm anticipating seeing a writeup on this exact topic from the ATSB with a few guidelines, but that being said, nothing has changed to warrant a change to the system.
We weren't there so we don't know what happened.