I follow every significant auction. Im well aware of what it sold for.
However the average sale price remains around $175-$200, so one sale does not justify raising the value to $500
I bet if you auctioned another one you wouldnt get much above $100.
I base that on the fact that if you took the winning bidder out of the equation that is all you would have got.

Anyway, it was still a very good result for you. Nice find.