Very few carriers use this method. Most use a method where they can sell as many seats are available at the joint price in each booking code. That one sells out, they go to the next higher price/booking code. This differs from say a cruise company that buys a "block" of seats and can use them as they see fit. While we all have our ares of expertise, this was at one time in my career, one of mine. Most airlines selling seats on each other, don't use the "block of seats" method, but instead query the operating carrier's GDS system for availability, and it gets returned a message. that may or not accurately represent the inventory of the operating carrier.

For instance, some carriers will display a maximum of Y9B9... while others will only show Y7B7 on another carrier. It all depends on how the way the systems link actual inventory. For instance, an example I used to see, is when carrier XXX queries UA, if UA has at least X seats (let's say 2 for this example,) then the marketing carrier will show full availability (say Y7B7) even if the operating carrier has only 2. Now if the operating carrier has Y1B1, it may trigger a "shut off valve" so that the marketing carrier shows Y0B0, while the operating carrier still has a seat. In this example, if marketing carrier books 7 seats when the operating carrier's flight is only selling 2, due to the "valve" being not triggered, negative consequences can occur. True, real time inventory between carriers doesn't happen, but displayed inventory follows a set of computer rules that vary by carrier and GDS systems involved.