The problem you run into with copyrighting quilt patterns is that it can fall into a useful item category and those can not be copyrighted.
That was already proven years ago when a dress pattern was copyrighted and then taken to court. You can not copyright a dress pattern.
Now as far as quilts well I guess that would be up to the judge at this present time.
As far as I know no one has successfully sued based on copyrighting pattens, nor selling items resulting from the items.
Check up court cases it is just not there that I can find.
Normally if there has been a court case involving a major pattern maker you should be able to find it in case law.
I wanted to add... I am not a lawyer I do research and look up things for fun.
Also I respect the copyright notice on a pattern. I would never copy a pattern and sell it. Once a pattern is bought and I made the item I would sell it if that was my intention but I do not sell items.