I never wash pre cuts. Fabric only shrinks in one direction. A jelly roll will shrink lengthwise not width wise. There is really no way to tell which grain way squares are cut so it's a guess which side they shrink. The easiest way to pre shrink fabric is to steam iron it or use starch to press it before cutting. No need to go through the wash cycle unless checking for bleeding. If anyone remembers the older issues of Quilter's Newsletter Magazine there were articles full of useful info about fabric, thread, manufacturers, and quality goods. I learned a lot from that magazine.