RCI's rules about using these certs are totally opaque.
I used my cert on a cruise I'd already booked that had a $300 OBC, but lost that and got a $100 OBC credit using my cert via the Club Royale # (the only way to use it) for a net gain of $550. I can use that $750 off a cruise that also has a BOGO discount, but it resets OBC discounts. Some of the cruise discounts can be combined. On a 7 day cruise, spending (losing) around ~$3500 playing blackjack, I'll get a cert worth $750 that I can use toward any cruise. I keep pretty tight track of my casino spending. There's also a $ value on the cert that can be applied to any cruise.
I've never used a casino certificate for a free cruise (i.e., the list of cabin category & cruise dates that are completely comped). Depends entirely on your play (how much you've spent in the casino).
