I'm not sure airlines reduce inventory for sale in RM software but I could be wrong. Certainly varying the oversell percentage (yup, I'd agree 10% is pretty close looking at some route load factors/bookings) but whe RM "shines" is in adjusting fares/buckets to maximize revenue in each cabin and on each plane. J0 (or notionally, JX) could mean each J seat has been sold and no more are available or it could mean no more are available for sale becuase the cabin has been oversold. X simply indicates how many seats/reservations may be made in a fare 'bucket', only an indirect indication of the actual number of seats available. Ideally you're hoping as an upgrade to see 7s; if you're looking for an op upgrade you want to see 0s in the fares/cabins 'below' you and in your cabin plus X > 0 ahead of you (better cabin); in that case, you also hope you've got status or something else (bassinet location) that's gonna help 'sell' you personally for the opupgrade. RM is finely tuned by plane, route, and time: if DFW-LHR (example only) sells 50% of premium seats within 12 hours of departure, that's gonna be more of a nail biter than ORD-PVG that sells only 10% of those premium seats in final 24 hours.

As a nonrev, I cannot see fare buckets (which is why I have EF for my AA/FF stuff) but I can see general loads with minuses (-) showing class oversells (i.e, generically, I'd hate to attempt to nonrev on a -2/-2/-1 LAXNRT flight, although without Mrs CRP, I'm a much more fluid traveler).