@msbernst @axz @karger I think there may be an interesting story about "preadaptation" — we had References: headers and even the "In article Joe Blow wrote:" convention long before anyone figured out how to do threading properly. The original newsreaders were all delivery-order, just like email was. nn actually was the first threaded newsreader, but Wayne Davison's "hunt the wumpus" patches to the most popular reader, rn, were what made it real (along with server-side indexing).