lot of the patterns from fabric lines will have not yet been tested. Also often for shop samples we don't prewash so as we construct the steam and heat from iron as we press can alter the dimensions it only takes a fraction to go from precise to OMG WHAT HAPPENED! LOL I also really read and sketch out and use the calculator to make sure the pattern makes math sense before cutting. Once the pattern is workable I send the questions and my solutions along to the contact email for the particular fabric. Of course this is why I have come up with my own patterns too.