Not only that, but due to limitations in 19th century surveying technology, the actual 49th parallel as measured by a high precision GPS+GLONASS+Galileo receive

Not only that, but due to limitations in 19th century surveying technology, the actual 49th parallel as measured by a high precision GPS+GLONASS+Galileo receiver is some dozens of meters different from where the practically enforced line is (such as zero avenue and its ditch in South Surrey/Langley, British Columbia where it meets Whatcom County, WA). If you go here and search for "B street, Blaine WA" and right click in google maps, look at the latitude, the actual 49th parallel is considerably south of what is enforced in practice. Much of Blaine, and a very long strip all the way to the great lakes, is actually in Canada... https://www.google.com/maps/place/B+St,+Blaine,+WA+98230,+USA/@48.9999487,-122.7422753,824m/data=!3m2!1e3!4b1!4m5!3m4!1s0x5485c403ae0fb04d:0x8ae175f7921379f5!8m2!3d48.9999452!4d-122.7400813 https://www.google.com/maps/place/B+St,+Blaine,+WA+98230,+US...