Submissions may be filed “at any time” under 35 U.S.C. 301. However, this period has been defined by rule (37 CFR 1.501(a)) to be “any time during the period of enforceability of a patent.” The period of enforceability is generally the length of the term of the patent plus the 6 years under the statute of limitations for bringing an infringement action (35 U.S.C. 286). In addition, if litigation is instituted within the period of the statute of limitations, submissions may be filed after the statute of limitations has expired, as long as the patent is still enforceable against someone. While submission under 35 U.S.C. 301 may be filed at any time during the period of enforceability of the patent, submissions filed after the date of any order to reexamine will not be entered into the patent file until the pending reexamination proceeding has been concluded (37 CFR 1.501(c)), unless the submissions are submitted (A) by the patent owner, (B) by an ex parte reexamination requester who also submits the appropriate fee and other documents required under 37 CFR 1.510, (C) in an ex parte third party requester’s reply under 37 CFR 1.535, or (D) as an enterable submission pursuant to 37 CFR 1.948 in an inter partes reexamination proceeding.
The purpose of this rule is to prevent harassment of the patent owner due to frequent submissions of prior art citations during reexamination proceedings.