I remember some such promotion going on, but it doesn't really matter if someone remembers the promotion. What matters is that your travel agent is able to get this straightened out with the cruise line. Did the agent make copies of the vouchers before sending them in? Does the agent know to which department s/he sent them?
If the agent doesn't have copies, my suggestion would be for the agent to get in touch with her "inside sales rep" to discuss the problem. The Sales Dept should have a record of the various onboard promotions that went on last year.