All I'm saying is that you can pick yourself which BTC purchases match up to which BTC sales, just like with stock.
No you can't. It's LIFO.
With stocks it is LIFO
unless you identify specific shares when you sell. I haven't seen anything to say that bitcoin will be different that stocks, but who knows what is coming next.
EDIT: Correction stocks are FIFO (not LIFO) by default.