Hello, so I found 4 scott 519 stamps all perf 11 and the from either 1917 or 1918. The dates are shown on the post cards, but for now I want to ask about the earliest one from November 26, 1917. When looking about on some of the auction sites I saw that one from a month earlier(second earliest scott 519 found) than mine, had sold for $3500. It was in great condition and so I was wondering how mine would compare. What kind of monetary price could this piece be worth.