booking through Costco

[JLitfin]

I've only reserved my RCCL cruise on the RCCL website or the Next Cruise Desk on board. I was wondering if I book on the Costco website would I receive the Costco gift card that they are advertising as well as the promotion the RCCL is offering at the time of booking.

or if I book at the Next Cruise desk on board, would I receive the Next Cruise onboard credit plus the promotion RCCL is offering at the time of booking, then if I move my reservation to Costco would I also receive the Costco promotion which is the gift card.

Thanks in advance.