This comment makes it sound like they sold private recordings to whomever was willing to pay for them, but they paid third parties to evaluate Siri recordings.
From the graph in the paper, it seems that once you make it till 60, the mortality rate is actually lower if you're famous. I'm guessing it's because the ones with an extreme lifestyle don't make it that far, and the famous singers have more money to spend on healthcare than the less famous singers.