I can only offer my recent experience in wanting to book something as a hedge against possible changes to prices and availability in the future:

• On 23 February, I used Qantas, Cathay, and JAL to locate award seats for an outbound trip in CX F on my desired date and called AS to book. AS found the same CX F seats and booked them for me.
• On 25 February, I also used Qantas, Cathay, and JAL to locate award seats for the return trip in CX F on my desired date and called AS to book, but AS couldn't see the CX F seats. AS found CX J on different (undesirable) dates instead, so I booked that.
• On 4 March, I again used Qantas, Cathay, and JAL to locate award seats for an upcoming trip in CX F on the same desired date and called AS to book. This time AS found the same CX F seats and changed my earlier booking to CX F.

In each case, the CX, QF, and JL sites all showed CX F seats available before I called AS. I'll likely never know whether those CX F seats were actually available when I called on 25 February or if it was a case of HUACA, but AS were ultimately able to see and book the same CX F seats I wanted, so I'm happy with that outcome. If I actually get to fly those flights in F, I'll be even happier.