The methodology used to determine accuracy involved loading GIS data on all property in a given county. Therefore building a nation-wide accuracy map using that

The methodology used to determine accuracy involved loading GIS data on all property in a given county. Therefore building a nation-wide accuracy map using that methodology would, by necessity, involve loading all property data nation-wide. And if you had all property data nation-wide, you wouldn't need a reverse geocoder. You'd have one.