One mph over the limit is a joke and would never hold up in court.
This is all you need to know. Last I heard, automakers only have to be accurate to +/- 3mph so there is no way that that anyone can get away with enforcing that.
Oh, and for the record, I will no longer go anywhere near Windor Heights and I am sure I am not the only one. If you own a business in Windsor Heights, you are getting screwed here.