I'm wondering whether it's worth also keeping track of how many people declined to join because we already had done so through other organizations. Might make you feel even better :)

FWIW, I joined through Marrow.org probably a little under 2.5 years ago. Have just remembered that I deliberately didn't get into their online system, so all my paperwork is, well, paperwork. But my card's on the fridge.

(Semirelatedly, it would be interesting to see how many folk who didn't give blood were "can't" vs "won't" -- I was on abx over the weekend, but for blood donation purposes I'm also considered a mad cow.)