I have 1890s & 1900s vintage scanned Topographic Maps. The Coordinate system is obviously a Geographic Coordinate system since only the lat/longs are represented in the tics. the datum is Mean Sea Level. Perhaps they are in Polyconic Projection and Clarke 1888 ellipsoid. based on the corner Tic coordinates they were geo-referenced to Datum NAD27 because of convenience.
I am not an expert in geodesy, but how much shifts are expected for such transformations? Is such practice acceptable? There seems to be no sure answer. Any guidance/help is greatly appreciated.