(a) The effective filing date for a claimed invention in a patent or application for patent, other than in a reissue application or reissued patent, is the earliest of:
(1) The actual filing date of the patent or the application for the patent containing a claim to the invention; or
(2) The filing date of the earliest application for which the patent or application is entitled, as to such invention, to a right of priority or the benefit of an earlier filing date under 35 U.S.C. 119, 120, 121, 365, or 386.
(b) The effective filing date for a claimed invention in a reissue application or a reissued patent is determined by deeming the claim to the invention to have been contained in the patent for which reissue was sought. [80 FR 17963, Apr. 2, 2015]