Ridley Park's Online Digital Community
The "simple" answer is that none of those streets were opened in 1886-(7), the year Ridley Park incorporated as a Borough (municipality). And the farmland that later became housing developments where those Streets are today was not purchased as part of the Ridley Park Suburban Town Plan. See Copeland town plan. I guess you never attended one of Keith Lockhart's History Slideshows about the development of Ridley Township, Ridley Park?
Ask Keith about it.
Good question -- it is very confusing. Keith Lockhart as Tim said is the expert here. In 1987 Keith published books on the history of Ridley Park and Ridley Township, which are available at the library.
The postal zip code system I believe was created pretty recently. A number of areas of Ridley Township were included in the 19078 RP zip, for some reason
You pay taxes to the municipality in which you live. It doesn't matter what your zip code is.
If you live in the Borough of Ridley Park, you pay taxes to Ridley Park. If you live in Leedom Estates, Ridley Acres, Milmont Park, etc, you pay taxes to Ridley Township; they are neighborhoods in the Township.
As you say, the zip code address system is much more recent than the formation of local Townships and Boroughs. It is an interesting topic; awareness of local History is important to understanding how the region developed.