That's correct. Some market makers close at 4 pm or just after on any particular stock. If a market makers who was on the best bid and best ask close at 4 pm or 4:02 pm then they show as closed with no bid or ask and the mm lineup and price changes to reflect the mm's that are still open, but it is effectively meaningless. NITE, UBSS, AUTO, ETMM do it quite often. There is no aftermarket trading on the pinks, just occasional T-Trades that were most likely transactions already determined during market hours but didn't execute until after 4 pm.