Why do you think the terminal would update (100's of symbols) that you aren't interested in?
On MT4: Unless the current chart is that specific pair/TF referenced, you must handle 4066/4073
errors before accessing prices.
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history in MQL4 EA - Forex Calendar - MQL4 programming forum - Page 3 #26 № 4
The function linked to, opens a hidden chart for the symbol/TF in question (if not already open,) thus updating history, and temporarily placing the symbol on Market Watch (if not already there,) so SymbolInfoDouble(symbol, SYMBOL_BID) or MarketInfo(symbol, MODE_BID) don't also return zero on the first call.
On MT5: Unless the chart is that specific pair/TF, you must Synchronize the terminal Data from the Server.
Is
it mystical?! It is! - Withdraw - Technical Indicators - MQL5 programming forum
Timeseries
and Indicators Access / Data Access - Reference on algorithmic/automated trading language for MetaTrader 5
Synchronize
Server Data with Terminal Data - Symbols - General - MQL5 programming forum

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in mt4 its possible to download server data and check many of symbols but mt5 dont update the symbol charts, and you must open it on screen and waiting for update!
so when i run the code, many of symbols data is old or chart is not available
and my exported file, created with wrong data!
is a way for updating data before or update in during code execution?
notice:
i want to check many of symbols ,NOT one!