I did discuss this with my attorney contacts...and the old plat is null and void in regards to lots that were not conveyed prior to subdivision and zoning and using those old lots now. That said, it is evidence in regards to lots that were conveyed. Also what was interesting is that the map had a little loop road, but the right of way of such would have not been created either. There would be an easement out off necessity/prescription, but no dedicated right of way (which does make sense).
Any re-subdivision now, should be required to dedicate the road in i's entirety. That may be in your favor should the proposed lots not meet 100% of the requirements. Be aware that the ROW width may have to be increased in areas not yet subdivided. A good portion of substandard subdivisions also had substandard road widths. What may have been adequate for a Private? ROW may not be adequate for a public ROW.
Paul in PA