If you have already washed the yardage I wouldn't worry about it. If you haven't, I would certainly not go to the trouble of washing it. I am another person who does not pre-wash fabrics except reds and flannels. I might get bit some day, but I am willing to take the risk. Since the precuts can't be washed before piecing, I don't worry about the yardage being pre-washed.
Pam