FIFO (the default expected by the IRS ) means that you must report as selling the earliest of your purchases. i.e. you use that acquired date and cost basis.
LIFO just means you are going in the opposite order.
There's nothing complex about it.
For stocks you can't use LIFO unless you have informed your broker that that's what you want before the sale.
For crypto, you don't get a 1099-B.
I'd suggest you stick with FIFO to avoid hassles with the IRS. Use your own judgement.
to answer your question, the date acquired must be before or on the date sold.
For stocks, additional purchase after can put you at risk of a Wash Sale. see the Wash sale rules in the IRS publication for more information.
