I have a clothing pattern out to pattern testers this month.
Of course after I had sent it out I found a couple of errors. Most were grading errors. Since the errors were things that the testers could correct themselves (like raising and lowering hems) I made a list of known errors and how to correct them and sent that out to the testers.
It was embarrassing, but that is what pattern testing is all about.
Once I get the reviews from the testers I will be correcting those errors and any new ones they find.
Now a lot can go wrong in grading. Grading can be a complicated process, it is not just making things smaller or bigger by scaling, nor is it just adding a set amount of difference everywhere.
It even gets a lot more complicated when you are working in historic pattern shapes that there are no modern grading rules for!
Mistakes are going to happen, and you, as pattern maker and grader, may not always catch them. This is why you get a good group of pattern testers to be the second, or third, set of eyes for you. Hopefully you catch all the errors in the testing phase, but if they don't, be good to your customers, include an addendum for errors that they can fix, or better yet have the page(s) reprinted. You do not want to be the pattern company who gets bad mouthed for having poor grading.