Actually, I might have been an edge case and not representative of their normal rules.

"The Reward is issued approximately 3 months prior to the member’s renewal date in a Renewal Statement and reflects rewards earned up until the issue date. A member must be an active, paid Executive Member when the Reward is earned and issued to receive the Reward. To receive a refund for the Executive upgrade fee the membership must be canceled or downgraded to a Gold Star or Business Membership and any 2% Reward issued or accrued will be forfeited. Any additional savings and services exclusively for Executive Members will be rescinded." https://www.costco.com/executive-rewards.html