I Think My Door Is Lying to Me

Oh the basement! Such an....interesting place. I can say that it is growing on me though. I mean, I still wont go down there at night though but I digress.... The basement level has a huge door that opens to the road. It's original to the house and hell if I know how to open the damn thing. So giant red door has the year "1781" on it.

Hi Door! And my shadow! Oh and look, another project! Note to self: do something with those wires!

My original assumption was that 1781 was the date it was built. WRONG! I checked the deed and the National Historical Registry and it turns out the build date is 1775! It's not the address, it's not the build date, so why does my door say 1781?? It does a great job of confusing delivery people but beyond being a pizza guy's worst nightmare, what does it mean??