True, but it helps to use deductive thinking. Since award inventories are can be accessed by almost any GDS (you just have to know how to do it), there's one single inventory for X, I and O class for each flight of each *A airline. However, UA MP isn't using a GDS for award reservations, they are using a customized *Net program version to access this inventory. And quite obviously, as shown by heaps of anecdotal evidence, this program has some kind of filter that prevents MP members to book (or even see) certain award seats or award flights. Some flights won't even show up at all. That means that the filtering is done at UA. In fact, UA could manually access and book any award seat shown in the GDS by using a longsell, but, as stated by several posters, they "aren't allowed to do that, anymore". Well, guess what? LH M&M agents will happily do a longsell in cases their *Net version acts up. Conclusion: UA is trying to reduce award inventory on non-UA metal. Which, btw, is the only scenario that makes commercial sense, anyway, as UA has to pay a premium for non-UA award seats, while the other *A carriers would certainly be happy to take UA's money in exchange for giving away an award seat.