What does an old atlas have anything to do with the article? Please explain your strange comparison. I can show you that it’s true because I have a newer map of Alaska. How’s that for the explanation.
You can read the Treaty: Google the Avalon Project
Sometimes these treaties are rewritten to better define a line. The 1783 USA/British Treaty defining the division between the US and Canada wasn't "accurately" defined until the Treaty of Ghent in 1814.