When the claims of a patent are substantially changed during Ex Parte Reexamination, Inter Partes, or Post Grant review, a potential infringer may be granted intervening rights, which to some extent allow practicing of the claimed invention.
Absolute Intervening Rights
Absolute intervening rights provide protection from past liability and damages. An accused infringer may use or sell a product that was made, used, or purchased before the grant of the reexamination, review or post grant certificate, unless such activity infringes a claim found valid in the post grant proceeding and which was in the original patent. If a claim is amended during a post grant proceeding and the amendment substantively changed the claim, then absolute intervening rights apply.
An absolute intervening right does not extend to infringing processes or methods. Essentially, an infringer may sell off existing inventory of a product that infringes the reexamined or reviewed patent claims without incurring liability for past damages.
Equitable Intervening Rights
Equitable intervening rights are an equitable remedy which may be ordered by a court to provide protection from future liability and damages. Equitable intervening rights address the continued manufacture, use, or sale of additional/new products covered by the reexamined or reviewed patent when the defendant made, purchased, or used identical products, or made substantial preparations to make, use, or sell identical products, before the date of issuance of the reexamined or reviewed claims.
Equitable intervening rights are potentially much broader than absolute intervening rights, but they are discretionary. A court may provide for equitable intervening rights to protect prior investments, including the continuation of otherwise infringing activity after such time.