A special assessment area may include any or all property within a project area as the project area existed on July 1, 1978, established pursuant to Chapter 4 (commencing with Section 33300) of this part, and may, but need not be, coterminous with such project area; however, only properties benefited by redevelopment activities described in Section 33814 shall be included within the special assessment area. The properties included in a special assessment area may be either contiguous or noncontiguous; however, only properties within a single project area may be included within a single special assessment area.