Wizofoz
In a CAT I, CAT II, CAT IIIA and CATIIIB-with-DH approaches, after we overfly the OM we are allowed continue the approach even if reported RVR gets below minimum. But we can only continue till the DH, at which we go around unless we have the required visual references.
what if there is no DH at all?
In CAT IIIB-with-no-DH there is no DH, only AH. There is nothing to decide, no point at which we have to see any visual references. So I guess we should overshoot as soon as the RVR goes below minimum, at any moment during approach. Or maybe revert to CAT IIIB-with-DH minimum and then decide at that DH, It occurs to me now.