Georeferencing a map of the pyramid complex of Djedefre, wrestling with inaccuracies, residuals and RMSE.

Georeferencing a map of the pyramid complex of Djedefre, wrestling with inaccuracies, residuals and RMSE.
What makes georeferencing historic maps difficult and how does the process work? Here I georeference a problematic map of Abu Rawash, pyramid and cemeteries, Egypt.