The motors in the bags are dated from different days in July-1970. I read somewhere the other day a rocket motor's shelf life could be decades if kept in a cool dry place where there's little fluxuation of temperature, humidity and so on. These kits came from someone I dealt with in the 1980s, who bought them new & kept them in such an enviornment. He actually works for NASA. I'd use one of these engines in my most coveted rocket w/o (much ) worry-mainly because I know where they came from & how they were stored. (ok-here comes tha criticism-ha). Several years ago, I actually flew a Centuri B3 - 5 & some Estes B8-4s from the 60s w/no problem-still have tha casings. But then, I flew some Estes A3-4t motors that blew a few rockets to pieces that were dated 1973. So its anyone's guess. When a motor fails like that, its mainly from a crack in the grain from these changes. dan.