The great gift gaffe

This past weekend T. went to a birthday party, and while I was digging through our collection of used gift bags to put the present in, I discovered one from T.'s birthday back in January. The bag still had the little gift card attached to it--you know, the card you never read because so many people thoughtfully leave it blank because they know you'll want to reuse the bag? And kids always seem to make their own cards instead of writing their names on those microscopic gift bag cards--I know mine do. But because I wanted to reuse the gift bag, I did read the card on Saturday morning, though--and the words: "To T., from D. Happy 5th Birthday!" struck terror in my heart. D.! D. didn't bring T. a gift! I know he didn't! Or did he? It's all a big blur now. I remember walking D. up the stairs to T.'s room on the day of her party. I remember how he looked up at me, earnestly, his blond bangs flopping into his eyes, as he said quite clearly and matter-of-factly: "I forgot to bring T. a present." I patted him and said that was just fine, because of course it was. D. and his mom left before the present opening, which seemed appropriate I guess--maybe she didn't want D. to feel badly? And when the time came to writing out thank-yous I mentally omitted D. from the list. Can you see where this is heading? Now I feel terrible. Many, many weeks--months--have passed since I sent out the thank-you cards. In my weak defense, the present-opening part of T.'s party was an exercise in complete chaos. Looking back on it all, let me assure you that no matter how on top of things you think you are, you will not be able to remember who gave your child which fairy princess Barbie when you eventually get around to writing the thank-you cards. Clearly I thanked the wrong people for the wrong things; I may have thanked someone else for a gift they didn't bring; and worse yet, I never thanked D.'s mom for the gift D. did bring. Help! What do I do now? Do I a) write a note to D.'s mom explaining the situation and apologizing for the error b) let it go and move on--I will probably never see her again after May c) send out some sort of blanket e-mail to all the moms apologizing for screwing up the thank-you cards (I know I thanked some parents for the wrong things). I don't know D.'s mom at all, so I can't laugh this off as I might with a close friend, or even a preschool mom I do know fairly well. I never see her at pickup, so I think the best way to handle this is by e-mail or with a note. I'm thinking option A is the way to go, but how do I handle this gracefully? What do you think? What would you do?