Airlines ( at the least the more advanced ones) have long restricted availablity by POS, so this no suprise or secret. MRU POS RTW fares are lower than many, so it's not unexpected your running into inventory availablity issues. POS of sale inventory limits are based on the expected revenue from that POS, so if the POS has lower fares, expect lower availability.

Also, to be clear, it's the individual airline (Not Amadeus, or any of the GDSs that determaine POS of sale limits for each segment). The carrier is betting it can get better revenue on the segmnet in question from another passenger, so has closed down the inventory for your POS. Availiblity in Amadeus is simply what CX is telling them to show available. Also, when you call CX direclty, they are not looking at Amadeus to see availablity. They are looking at theire own CRS that they internally maintain.

POS is a fact of life when flying..especially on discounted Alliance products. Your option is to pay a higher fare or wait until the available dates..unless you can convince somone to overide the availiblity..wish I would rate as a slim chance. Inventory can open up closer to depature, but I wouldn't count on that either given the loads expected this summer.