How are Ex Parte Reexamination Certificates numbered?
Ex Parte Reexamination Certificates are numbered using a specific system that includes both ordinal numbers and ‘kind codes’. The MPEP explains:
The ex parte reexamination certificate number will always be the patent number of the original patent followed by a two-character “kind code” suffix. The first letter of the “kind code” suffix is “B” for reexamination certificates published prior to January 2, 2001, and “C” for reexamination certificates published on or after January 2, 2001. The second letter of the “kind code” suffix is the number of the reexamination proceeding of that patent, and thus shows how many times that patent has been reexamined.
For example, if a patent undergoes its second reexamination, the certificate would be designated as ‘C2’, indicating it’s the second reexamination certificate issued for that patent.
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