Unless it has recently changed, coach has no time limit on returns. I fact, if you have the receipt, they will give you full credit. I think the only exception. Is if it was a factory purchase. But even then, if you have the receipt, you would be fine and get full value. Have you tried calling the coach store to tell them you have the bag and the receipt? I'm sure they could give you more details if you wanted to pursue that option.
Good luck - I'm sure it will all work out well

and how nice of you to gift such a great bag!