We used to only gamble in Vegas and very little on any cruises (as we had no luck).
Maybe this has changed since the pandemic. Can you explain further? Did you meant to imply the card said you had a comped cruise offer and you went down to the Next cruise office and got a quote on a specific cruise you wanted to go on and it was a good discount but not fully comped? Also maybe you didn't explain it thoroughly but I'm not understanding what exactly was the offer on the card? Your statement is a bit contradictory and maybe for brevity sake you omitted some details.
My husband has been with BCC for years and has NEVER received any kind of onboard offer for a free cruise on a Celebrity ship.