I would like to understand why the data reported as "PREV CLOSE" via NYSE (probably also other sources) is invalid over the weekends. One would think this would contain the value from the Closing price of the previous Trading day, regardless of the date you reference it. Note: Service providers such as TOS merely pass this garbage on as "CLOSE" price via RTD, or "Yesterday's Close" via their Watchlist. (TOS merely does GIGO {Garbage In Garbage Out} with this data). -- Response from TOS (Yesterday's close price, on the other hand, is the data provided by the exchange. This means it will reflect whatever the exchange does with the data.) Currently TOS reports SPX close (via RTD) as 2113.32, when Friday's close was 2037.41. The reported value is Thursday's close. If someone can provide insight on why this data is unreliable at times, I would like to hear. This information reliability is not consistent across underlying's.
Unfortunately the response from TOS is a POS. Surely they would be storing the data points and reporting on that. If the exchange is reporting it wrong and they are using that, they need to show why it is the exchange at fault and detail what steps they are doing to ensure that the data they show is correct.
jharmon: IMO: My issue is not specifically that the exchange is reporting "it" wrong, but a nearly useless value with update intervals preventing it to be useful unless market is currently open. The value updates each trading day at undisclosed times. This means Friday's update relates to Thursday's close. They will not report Friday's close (for all symbols), until Monday (or 1st trading day of the week). Sometimes, the value may update earlier, but not guaranteed. Also, another issue, is if the date is Ex-Dividend day, the value will be decreased by the amount of the dividend, which is fairly useless. <-- IMHO: I would prefer TOS to merely provide the prior trading day's closing value {Instead of the weird value from the exchange}, which is updated by midnight of a trading day. (So the weekend would contain Friday's closing price). They already have the closing values available at market close (note their Charts always report the correct closing prices for all dates, including the prior Day)! --
Sounds like you need to subscribe to a data vendor. Brokers never do data quite right and they don't care (i.e. not core business)