Your analysis is too simplistic. Yes you can take a cost basis. I simply leave them two different positions for calculations purposes. But if you want to take a cost basis you can by simply figuring it out.
Lets assume Stock A was $5 when PSL 21 Started.
After some time Stock A decline to $2. You decide to sell stock B to DD. Stock B was up 50% when you sold.
Under that scenario 200/$5 and 750/$2= Cost basis Would be $2.63
If stock B was sold unChanged when sold. The cost basis would be $2.86. So the point is stock B performance when it is sold determines the cost basis. Hoep This Helps.
A great way to verify your cost basis and determine the sales methodology when that time comes is to use the technology that is out there. Just plug in "cost basis calculator" in your search engine you will find it. You don't want to just guess your cost basis because the new regulations hold individual investors responsible for getting it right.
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