Sorry you had to learn this way... :(
Most all fabrics will get stretched slightly off grain when washed and dryed, especially during the ironing/pressing process to get the wrinkles out.
When making a OBW/S&W type quilts, the slightest grain variation in the fabric will throw the fabrics designs off. These are what you line up in these techniques, and they need to be spot on :D:D:D