Was it shrinkage? Could be, but 3 or more inches across the width of the bolt? Things always seem to shrink in the length, not the width. So I took out a couple more pieces of fabric I'd bought very recently and measured those. Less selvages, they both measured 41" wide. Okay, that's better but still a little skimpy.
When I was a kid, my mother used to buy canned food--vegetables and whatnot-- in a 16-ounce can. Now you buy those same products in cans that are 14-1/2 or 15 ounces. I did find one can in my cupboard that was 16 ounces, a can of refried beans. Actually, I think the can is the same size, and the manufacturers are putting less food in the can and charging the same price. I'd guess the same thing happens nowadays with cereal and lots of other things.
All my recipes still call for a 16-ounce can of whatever, but I haven't bought a new cookbook in a while. Most of my older patterns base yardage estimates on fabric that is 42"-44" wide; but I looked in a new McCall's quilting magazine, and they based the estimates on fabric 40" wide. Okay, so maybe I haven't been paying attention. What's the moral of the story? I don't know, pay attention, I guess!