I don't think you need the amounts to write the thank yous. I never have included amounts in the thank yous when given money. Do you still remember who gave you gifts or is it just the amounts you can't remember?
Who gave money. Some people came with just a card and no gift so I can't eliminate who gave items and just blanket thank the rest with money thank yous. Also some gave gifts AND money, like DHs grandmother gave 2 very cute outfits, but I can't remember if she also gave money in her card or not. I wouldn't want to leave that out of the thank you card.
Lesson learned, do not leave DH in charge of....anything lol.