my co-workers threw me a shower. i know work paid for the shower, but co-workers contributed individually to the gifts.
the problem? i do not know who contributed. there is a signed card. not everyone invited to the shower attended, but all invitees signed the card.
do i send thank you notes to everyone who signed the card (and assume they contributed to the gifts), or just the people who attended the shower (and assume people who did not attend did not contribute to the gifts)?