@trneaville , fundamentally , this is no different than acquiring multiple batches of the same stock over the years ( except that the split creates new stocks / daughters where each stock is worth different --- original investment divided by the new total number of stocks --- i.e. a basis adjustment ). Thus when you dispose off the stocks your basis is different. This is in contrast to adding new stocks where you need to keep track of basis for each acquisition i.e. each batch and when you sell you have tell the broker which batch you are selling , else it is assumed to FIFO.
Does this make sense ? Is there more I can do for you ?
