Tom,
Your mission, if you choose to accept it, is to find the one Topo map that really matters, whether it was the first or not....
Or, failing that, to find that HDC Property original subdivision map, which is the yin to the yang and should tell the story by revealing the opposite border.
May the force be with you.
It's miracle time in Philadelphia this week. There is still enough magic in the moonlight for you to accomplish your quest.