They've been out there KW. eBay
isn't the only place they sell and values range depending on bidders, etc. It's nice to see the two latest have apparently sold high.
BTW, (++) indicates significant increase over the base. A single (+) means some increase.
I still don't know about the OP's piece being worth the $500 in condition being tinplate and not porcelain. But as I said, I'd happily sell one for that kind of money in that kind of condition.