Sorry I'm confused as well.

Economy is 'm' - Eurobudget or 'y' - full economy flexible. Check in stub will frequently say 'm' regardless to denote class of cabin ie one class.

'c' is Club if separate cabin is available if not 'y' is highest cost of fare giving full flexibility.

My experience is that I cannot buy a 'c' ticket unless the cabin is available.

To further add to it I frequntly book D2 tickets which are business class fares available where a separate cabin exists and which are sometimes less than the 'y' economy fare.

The restriction being the linitation to the same airline.

In my experience in Europe the cost relates to flexibilty and then to cabins available.

No 'c'class in Europe, not sure I agree with that. If it dosn't exist why are we all paying for it?