I am 99.9% sure the IRS has no system in place for crawling the blockchain, linking addresses to real people, or linking transaction times / amounts to bitcoin prices at that time. Hell i doubt they even have a division formed for this. In fact, given their reticence with virtual currencies as a whole, they are at basement level at best.
It doesn't need to. That's why you need to keep tax records for 7 years. You provide the records if they challenge your claims on the return.