it all depends at which market center your order is resting, and if opening auctions are reg nms protected or not (i don't know, but maybe someone else knows).
Please correct me if I'm wrong, but AFAIK, opening and closing trades are not "covered orders" (since thy require special handling) and thus exempt from RegNMS.
ah ok, so in this case, if the order is resting on a certain marketcenter, and another marketcenter's opening auction prints $0.50 below your price, there is nothing you can do. but if the order was on that marketcenter which had the opening auction priced $0.50 below, you would have gotten that $0.50 below price.
Not sure this is true. My understanding is that open/close trades are traded through and hit the book of a particular exchange - no routes to other venues because of RegNMS.
look, all I know is that my spouse had a limit order to sell shares of stock at 101. It opened at 102, the brokerage co. said too bad, they didn't fill at 102 becuase they had too many other orders waiting in line to be filled, so we got the price at 101, not 102, tuff luck!