Question from Keith S.:
Why do patents get reissued?
Patents can be reissued for a number of errors. The original error must have been an accident or mistake. The error must not have been intentional or purposely deceptive. Errors which can be corrected by reissuing a patent include defective drawings or specifications, improperly referenced documents and claims which are either too broad or too narrow.
Patent claims which are too narrow may not provide all of the protection which is entitled. Broad claims can invalidate a patent. To broaden the claims of a patent, the reissue application must be filed within two years of the date the patent was granted. An application to narrow the claims may be filed at any time before the expiration of the patent. A reissued patent does not change the expiration. The patent still expires twenty years after the original granted date.