is there any way to verify at this point?
Don't think so. You might have to fight for it but the T&C's are pretty clear.
8. Double First Year Cash Back:After the first 12 consecutive billing periods that your new account is open,
we will double all the cash back rewards you've earned and apply them to your account in the next billing cycle. You've earned rewards when they have posted to your account by the end of the 12th consecutive billing period. You will not receive Double Cash Back if your account is closed or no longer in the cash back reward program as of the award date. This promotional offer may not be offered in the future.