Greg did Marshall always rely on you for rides to Arneson's? If so that pretty much rules out any early Blackmoor games for "Marfeldt" since you would have been there and known about them.

I believe that I drove him to all of the sessions I was present at, but I don't think I was present when he and Dave clashed (or if I was, it wasn't obvious that it was happening), so he may have gotten rides to other sessions that I was not present for.