This is a really interesting project, and one that Polaroids suited perfectly. Being instant, you could take a picture then immediately write a date on the back. It's also very sad when you understand the story.
A number of years ago, I met a photographer online named Richard Wanderman. We exchanged a few pleasant emails/messages through flickr, and I lost track of him. Early this year, I thought of him again, and found his flickr account's last images were of him in hospital. I immediately searched for him online and discovered that he lost his battle with cancer only a few months before. Apparently, he was a very active photographer and computer guy, and many people mourned his passing. Who knows how many other flickr accounts hold similar stories?