If they are shearing prior to rolling, are they checking to make sure they shear square? I've had guys measure end to end and not be square corner to corner and the roll seam will be off. We generally CNC cut the entire sheet if possible so all is straight and square. Now that you have me thinking about it, I recall a job on some vessels we built where my material came in from two different mills. Both were A36 however one batch from one mill rolled correct according to my calculations but the batch from the other mill every roll was slightly different. I think something was off with the material and it reacted different .