Patent Search Limitations
All U.S. patents and U.S. published patent applications are filed electronically in a computer database, where searches can be performed based on keywords and classification. However, keyword searches only cover from 1976 onward, while classification searches can range back to 1790.
Furthermore, the database is maintained by the United States Patent and Trademark Office, and although they try to accurately update their records, sometimes problems, such as missing paper files that have never been encoded digitally, do arise.
Lastly, regarding U.S. patent applications, only published applications are filed electronically in the database, and as such, unpublished applications cannot be searched.
