MikeHotel152,
The worst case scenario would be that if CAT I holds were used up until the RVR dropped to 550m, then a departing a/c holding at the CAT I hold would get 'trapped'.... just when you need the CAT III protection. The solution is to move to CAT III in advance of needing them.
Some airfields need to have the CAT III stop bars manually inspected to ensure they are operating correctly before LVP initiated.
We go to CAT III holds at about 1000m RVR.
Surely if ATC are telling you "LVP not in force" then you know you cant do a CAT III approach?
LVP in force, CAT I, II, III.
LVP not in force, CAT I only.
It has to be that simple.