Demandt's work was also translated (Colin. D. Thompson; History that Never Happened: A Treatise on the Question, What Would have Happened If—?, McFarland 1993). Definitely worth reading.
I remember Clancy himself (who was active on old usenet) becoming very aggressive when (usually veterans) pointed this very point out to him. In the shiny world of 90s/80s technothrillers, western hardware was supposed to work perfectly.
I may be wrong, but I think I've heard on a conference some time ago that the early warning community was well aware of potential meteorite related events (not necessarily the very big ones, but at least smaller stuff). Actually, there had a decent overview of near Earth debris before the...
Regarding the 17th September 1918 event - a nice real live example about an impact this size is the Ries crater in southern Germany (always worth a trip). 15 my ago, but you still have a circular >20 km structure stamped into the swabian alb, with tens of meters of ejecta still covering the...
The genre was possibly already well developed in the 70s - see Alfred Coppels Thirty-Four East (1974) and The Dragon (1977). And Forsyths The Devil's Alternative (1979), Erdmans Crash of 79 (1976), or borderline cases like Avalanche Express (1976). Maybe also Hacketts first attempt should also...