In reply to robert-hutton:
I've a couple of 4 season down bags from thenabouts... A '77 ME and an '86 Salewa one. Along with an '81 Point Five Freney Goretex down jacket.
One thing I notice is that the outers were thicker, heavier and bulkier than anything around today. Longevity comes at a weight & bulk penalty it seems. I wasn't aware of it until I packed my old bag instead of a recent PHD one and had difficulty accommodating it. Rucksacks were bigger then too .
Progress, I suppose...