Originally Posted by
fumje
Checking for space will tell you if your upgrade can clear but the computer did not execute on clearing it. Frankly the waitlist process is broken, and for no status passengers it may leave you behind if you miss the space opening. (If you see pz, call in to request clearing.) The most likely times for space opening are around 1mo or 1wk.
You can hold off of checking if there is no p inventory (P0).
Funny enough last year had the strangest occurrence on my lax-lhr flight a few days before departure where availability was J5 JN5 C4 D0 Z0 ZN0 P0 PN1 PZ0. Never saw anything like it before, never seen anything like it since.