Where two or more nonconforming lots, held in one ownership, created and remaining unaltered since August 11, 1975, either legal or equitable, or subsequently come to be held in one ownership, and the lots are not created by an approved subdivision, they shall be considered a single lot of record for the purpose of this chapter, and provisions of this chapter shall not thereafter be circumvented or avoided by the willful sale or conveyance of a part or portion of any parcel or parcels.