I'll bet you're right. I forgot that in the USA we write dates reverse of Europe, so to us 11/9 is Nov 9.
It's very generous of you to not blame Europe. It's quite possible that your method is more correct than ours.
Just found this:
Why is the most common date format in the US like mm/dd/yyyy , whereas in Europe (including the UK) it's more common to have dd/mm/yyyy?
Looking around, I found that the US form is actually the more traditional Anglo-Saxon way, but the British adapted to using the European form in the early 20th Century.