The price of most stock changes constantly while the market is open.
If you buy 100 shares at 20.00 and 100 at 15. you can sell them separately or together since your cost average is 17.5 for 200 shares. You wait until you hopefully make a profit, like 21.88 will give you 25%.
(minus out commissions and any fees)
* What Id do is sell the 15$ shares at 20. or above and wait to sell the 20$ shares at 25.00.if possible..., not only do you make more but lets say you sell the 15$ shares at 20. and the market goes back down to 17. , you now have money to buy more shares.
* to answer your question, I use a broker so my statement indicates everything I buy and sell , the original amt.and the dates(I do buy systematically as well which means $200 each month buys a number of shares, I get told at the time what those prices are - they have to maintain this data for taxes)