Over the last couple of years the USPTO has introduced several new kind codes on account of changes arising from the America Invents Act of 2011. They are

1. F, Supplemental examination certificate
2. J, Post grant review certificate
3. K, Inter partes review certificate
4. O, Derivation certificate

These codes are for various types of certificates that are appended to patent documents. Other types of certificates include reexamination certificates, represented by kind code C, and certificates of correction, which are not assigned a kind code.

New certificates are announced in the Official Gazette of Patents. According to the USPTO database, as of September 8, 2014, eight supplemental examination certificates (Fs) and six inter partes review certificates (Ks) have been issued.