How to find out the validity of American patents?

Bibliographic data application number: 07/574,529 Customer number:-submitted or 37 1 (c) Date: 08-28- 1990 Status: Patent case application type: utility model status date:12-26-1. TIMOTHY F Location: Electronic Group Art Unit: 2402 Location Date:-ConfirmationNo.: 8452 Earliest PublicationNo.:-Lawyer CaseNo.: 2397/790 (FR) Patent Release Date: 02-26- 199 1-Invention Name: Electric Cooking Appliance This is provided by the State Bureau of Fine Arts. The validity period of American patent is 20 years, and the filing date of this patent is1August 28, 990, counting from the filing date. So this patent has expired and should not be renewed. This technology was 20 years ago.