it might depend on if you entered them all on the same day.

for stocks, you can match your buys to your sales to achieve your goal. that is, you can match today's sale with a real old purchase (pretending you deliver older certificates) or, a newer purchase. maybe you are gifting securities to a charity, for example. or, one match would be a LT gain and another match a ST gain. You choose your cusip. It's all about tax angles.

i would expect you may have to tell your futures broker what you prefer and he will tell you to screw off. such is the business is these days. It really means nothing as all are taxed the same way and marked to the market at 12/31 each year.

:-)