Its great that you know how to spot them. Just think of the ones who are trying to follow directions and have no idea that the reason it isn't working is not due to them making mistakes but the pattern maker. I take serger classes, we just used a book and thank goodness our teacher knows sergers so well that she could spot the mistakes and mark them. Even with that, I found a mistake as well, the only reason she hadn't found that one was because it was during construction and since she knew how to do that she didn't pay as much of attention. At least now you know to pay more attention to see if there are any more mistakes before you find out the hardway. Good luck