This case has always broken my heart as well. I too was a grateful dead burnout
I never followed them far, loved showers too well for all of that..But I went to about 11 shows throughout the southwest.
I also stopped going in '93, so I would not have run into Jason unfortunately...but I met and knew so many people like Jason, the only thing shocking to me is that there are not more UID like him. People who dropped out of society, and whose parents just wrote them off when he didn't come home. There were so many fringe people in the parking lots making veggie burritos.
I bet Jason had a backpack that is missing-which would explain the lack of id and wallet. Alot of the shows you would be required to show ID to enter..enough of them that you would def bring it with you as to not miss the show. All the boys I knew carried backpacks, so they had somewhere to stash all their clothing/wallet/copy of "on the road"/dope.
I do believe that Caroline(s) met Jason at the show, either that one, or an earlier one. I believe they either gave him a wrong number and a "happy" note, because they were supposed to hook up with him, and didn't want too. They wrote the note because they were too nice/well brought up to just leave him (perhaps waiting for them, if they were supposed to meet up), and wanted to leave some sort of contact on the chance that they run into him at the next show.
Sorry, no new info from me..just personal recollections of a fuzzy time in my past.