If you are doing UNIT counts then downloads have there value but if you are looking at sales then you have to look at revenue. Elvis Presley has been credited with 1 billion records sold which is completely crazy and not close HOWEVER they used a little record industry trick which is equlivent sales. the took physical singles sales and converted them to be album sales and doing that turned 200 million single sales 260 million album sales into a billion. the true numbers began to come out in 1958 with the invention of gold certfication and in 1976 with platnium cerification all based on $.but that changed as well when prices went up so they used actual sales. As far as my info I in a previous life was a music historian who had access to actual sales numbers,shipments and returns for close to 250 musical acts. I was a subscriber to Neilsen,Soundscan and I had access to record labels REAL numbers not press release numbers, I had court documents with real numbers from Motown,RCA,Capitol,Cbs when lawsuits were filed for royalties. I had so much shit it was crazy. I update numbers periodically thses days but album sales suck ass so its not worth it anymore to do it.