You cannot ascertain that the lower classes mean that the cheapest are gone, the ascends upwards towards Y on CX.

CX has different class codes according to each market.

For example, for tickets ex-USA, the majority of the inventory CX goes towards H class as that is what the discounted economy class literally most fares CX sells under. The remainder would be for other people who originated from elsewhere.

For fares ex-Singapore for example, majority is in M class for special 2 week tickets. 1 year validity tickets are sold in K class. It used to be in B class. But during peak holidays, that inventory is shifted to L class.

So basically how each class code shows up on the reservations system cannot reflect what is actually being sold. CX in turn actually 'holds' off a number of seats in all economy class codes till x-days / weeks prior to departure to maximise revenue.