Sew interesting! I used some blue fabric I bought In 1980 in two quilts. For some reason, that blue fabric broke down and disintegrated in both quilts -- it was only the blue. I am sure it was 100% cotton. I think it was the dye because I didn't have a problem with any of the other fabrics, all bought at the same time and place.
I think sometimes the production process go awry and there is no way of telling which is good and which is bad.
But, in your case, I am happy the quilts have brought so much happiness to your family.