Did you know that patents expire after approximately 20 years after the date it was filed? (in cases priors to 1995, only 17 years). So even if a design has been patented, it must be renewed every 20 years.

More information on this topic can be found at the United States Patent and Trademark office website:http://www.uspto.gov/web/offices/pac/mpep/documents/2700_2701.htm