@Glyn *******
a Non-O visa is not the same as a Non-OA visa.
A Non-O visa is normally only single entry, and you need a re-entry permit to keep it alive when you leave the country.
A multi entry Non-O only allows to stay 90 days at a time (and you're unlikely to get another one)
A Non-OA on the other hand is multi entry throughout its validity.