So again if the equipment at ADL was able to support CATIIIB the crews could have legally continued and landed
No. If you got the TTF that had Fog on it at the time you were landing you have to either recalculate from that point to ADL and then to a alternate or recalculate your position to ADL and then to the FM period that it improves.
Or divert straight away.
If you can't do any of that you then have to declare a PAN and do whatever works.
For CAT III to work we will have to have compulsory alternates. Until Australia brings that in CAT III won't do much.