Jaba, the quilt that shrank was made out of top of the line fabric, and I didn't prewash, I rarely do even now. I now usually take into account shrinkage if I'm going for a certain size, which I didn't way back then. I don't use cheap fabric just for that reason. As time goes on & the more I sew & quilt, I find fabrics in my stash I must have purchased 20 years ago, they are not the same quality fabric I will only use now. Guess one can call me a fabric snob, but whether I'm making something for myself or someone else I want the quality to be top quality.
I think all quilts shrink more than we realize, even those that are prewashed tend to shrink a little. It comes from repeated washing & drying, though times I will place out on cloths line. Only ones that won't shrink are those made for wall hangings & never get washed.