All airline availability displays include any overbooking profile (percentage) that Yield Management care to place on the figures.
When some flights are opened for sale, around 360 days before departure, there may well be a 100% overbooking profile placed on say, Y class. This is reduced as the flight gets closer to departure, and even then the flight can be 10% or more! I once did an exercise on how many seats were actually booked and later cancelled on various flights before arriving at the actual load factor after departure. The answer, as you can imagine vaires enormously, but can run up to several hundred. Yield Management know this and that is why they can adjust the overbooking profile accordingly, very often based on 'natural wastage' ie seats booked and then cancelled!
Personally, I never bother with even looking at all the sub classes as they are a waste of time! Just look at the 'parent' or 'zone' or 'compartment' classes of F, J, W (for World Traveller), and Y. All the other classes are subordinate and irrellevant! In Europe use C instead of J.
Having said that, I'll repeat, very often all of these compartment codes will still have an overbooking profile on them right up to check-in. Most of the time these flights clear and go full, or even light. That's the whole reason for the Yield Management Department - their job is to get the flights as full as possible!
Per Ardua ad Astra! ........ Honi Soit Qui Mal y Pense!