Are the books working the same way in pre- & post-market as they are in the day time market?

External question — Personal Finance Stack Exchange Author: Alexis Wilke Original post: https://money.stackexchange.com/questions/167919 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. Quite often, when I look at my orders in the pre- or post-market, I see what looks like discrepancies. Here is a screenshot of one set of opened orders in my account: As we can see, I have an open Sell order at $9.75 and another at $9.80. I could understand that the $9.80 doesn't sell. Someone else may be ahead of me. Makes sense. But I don't understand why the $9.75 is still open and not sold when the Last Price clearly says $9.80. Similarly, a bit sooner, the Last Price was $9.62 and my buy order at $9.65 did not go through. Could this be because the pre- & post-markets do not work like the regular market and someone selling at $9.80 will sell ahead of me to someone offering $9.80 even if they entered their order after my $9.75? Or is it that the precision of the pre- & post-markets is abysmal and the data shown is funky? Note: I understand there is (a lot less) volume and price can fluctuate much more (for smaller tickets). But that would not explain why my orders would be ignored. P.S. The screenshot is from my Charles Schwab account, although I've seen such discrepancies on my Ameritrade & e-Trade accounts, and also on the Yahoo! and Google Finance pre- and post-market screens. Update: here is a screenshot from Think Or Swim (TOS) with Today's numbers. I still had an open $9.75 sell trade since it went up to only $9.74 during the day. The first move just after close shows $9.76 as the max. and yet my $9.75 sell order did not go through.

External answer — Personal Finance Stack Exchange Author: Bob Baerker Original post: https://money.stackexchange.com/a/167923 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. NBBO requires that brokers find the highest bid price and the lowest ask price for a security across all U.S. exchanges. The discrepancy that I see is that if there is an order to buy at $9.65 and an order to sell at $9.75 then the quote should be $9.65 x $9.75, not $9.62 x $9.80. I'm assuming that the bid and ask volume quotes are for round lots. It's possible that Schwab is providing bad data. And if you have seen this simultaneously on multiple accounts then the problem is likely the provider of the data feed to the brokers. The last price of a trade has no relevance or influence whatsoever on current orders. That is history. The only determinative factors are the current bid and ask as well as the respective volumes at those prices. Time and price priority for round lots in the premarket and after market is the same as for the regular session. No one is sneaking in front of you.