Very little I would have though nannysue.
I agree that sometimes the things they flag up are misleading. I have seen this too but it has usually had the proviso, in this room category, or similar. Sometimes they allocate certain rooms for certain occupancies, so again it could mean 2 of this type for 2 people etc.
I am not defending FC but it is possible that at the time you booked they did only have 2 of that type at that price left. Sometimes they do get more rooms added onto their allocations and sometimes they change the occupancy levels.
It is not just an internet thing. Some friends were told in the high street that they had got the last 2 rooms but the website was showing availability for months.
Unfortunately I really don't think you would get anywhere with this, but nothing to stop you trying.