If you have US tickers as output from e.g. Compustat index constituents and you want to get stock prices from Datastream that’s possible. You can use a ticker to create a Datastream mnemonic. You have to add country code, so “U:” would do the trick. You can easily do this in Excel by concatenate U: with the column with ticker.
This solution works fine for all but the Nasdaq firms. Those will need a “@” sign in front not “U:” So just to be sure you have everything and you don’t miss any data do both so a list with “U:” and one with “@”.
The ones that don’t make sense will give errors but this way you won’t miss any. So with Ford U:F will work and give data, @ F won’t it will give an error. Similarly Micosoft @MSFT will work and give data, U:MSFT won’t it will give an error