Once they start a fabric run, if the fabric is not squared up properly on the machines, the whole run will be off grain. I once bought a panel fabric that had squares. I bought the same fabric at 6 different stores thinking that of them would have the printing on grain, but all of them were off grain. Finally one shop told me about how the mfgs aren't always careful to get the fabric straight so the whole run would be off grain. So the squares were rhombuses instead of squares. It seems that the fabric nowadays is always off grain at least a little.