ExpertFlyer doesn't have capability to search Cathay. It's one of a very small handful of the big airlines ExpertFlyer's software doesn't support searching for (Delta is another big omission).

That said, I'm not sure how you're looking for O class inventory on this route (or any Cathay route).

I'm also jumping on the free ticket offer and have likewise read the T&C to mean that there's limited inventory -- and also embargo/blackout dates -- in O class. I've also interpreted the first-come-first-serve policy to mean those who know, ahead of time, which dates/flights have O class inventory and get their payment processed will be those who will score the free ticket.

Otherwise, if you're on the site stuck searching 10, 15, 20, 40 different dates chances are the by the time you find one with O class inventory all the freebie tickets will be redeemed already.

My guess is that all these promo tickets will be fully depleted by 5:05PM PST, mere minutes after they go on sale.

Lmk what site/tool you're using to identify O-class inventory ahead of time?