I'm earning a Masters Degree in History and am researching a Revolutionary War fort that was burned by the British shortly after the Battle of Long Island. The fort would have sat in present-day Brooklyn in the neighborhood of Red Hook. I've taken coordinates from a map that was surveyed and created by British Naval Engineer Bernard Ratzer in the late 1760s and, after adjusting for scale, plotted them onto a modern day map of the city, using the same landmark location on both maps as a common anchor point from which to measure. The anchor point is about two miles away from the location in question. My resulting data put the fort approximately 550 feet (about 167 meters) away from the currently-believed location (and some distance into Buttermilk Channel. I repeated the procedure, using the 1776 Henry P. Johnston map and a few others, with similar results each time.
My question is, would this 550-foot discrepancy fall within the expected margin of error when using a point 2 miles distant for reference, considering the surveying methodologies of the time? Or would these results give reason to doubt the currently-believed location?
Attached is an early illustration. Thanks for any information you may have to offer.