Flew into Dublin one night with it reporting overcast at 100 feet, the visiblity was fine, just low cloud with LVPs in force.
Anyway they cleared the aircraft ahead for a CAT II approach (R28 is CAT III), thought nothing of it untill another aircraft ahead asked was CAT III available, to which approach replied that the Mid Point transmissometer was U\S and he could only offer CAT II. There's noting in our OPS manuals about this, so I don't know what reference he was using.
IR