Checking my Nerf MA40 redeem code

I just remembered that the Nerf MA40 I got comes with a redemption code. I just tried to enter it and it says the code has been entered the maximum amount of times. Is this showing because I’ve already entered it and don’t remember? On the card it says codes only valid for a limited time so would that be why? Is there any way to check what codes I’ve redeemed in the past?