No part or portion of any lot which is determined by the Conservation Commission to be a coastal or freshwater wetland, as defined by the Wetlands Protection Act (MGL c. 131, § 40) and the regulations promulgated thereunder (310 CMR 10.00), shall be used in determining minimum lot size as required herein, except that this subsection shall not apply to any lot lawfully laid out by plan or deed duly recorded, as defined in MGL c. 41, § 81L, prior to the effective date of this subsection, to any lot shown on a plan endorsed, prior to the effective date of this subsection, with the words, "Approval under the Subdivision Control Law not required" or words of similar import, pursuant to MGL c. 41, § 81P, or to any lot shown on a definitive plan endorsed with the words "Approved under the Subdivision Control Law" or words of similar import, pursuant to MGL c. 41, § 81U, which complied at the time of such recording or endorsement, whichever is earlier, with all of the minimum area requirements set forth in the Zoning Bylaw, except for this subsection; provided, however, that this subsection shall apply to any subdivision under the Subdivision Control Law, aforesaid, submitted to the Planning Board on or after the effective date of this subsection.