Once again, here's a link to the most recent numbers from Nielsen SoundScan. These numbers are more recent than the earlier articles you both referenced.
Nielsen SoundScan describes itself as an "information system that tracks sales of music and music video products throughout the United States and Canada. Sales data from point-of-sale cash registers is collected weekly from over 14,000 retail, mass merchant and non-traditional (on-line stores, venues, etc.) outlets. Weekly data is compiled and made available every Wednesday. Nielsen SoundScan is the sales source for the Billboard music charts."
Sales figures quoted in news articles may or may not be the latest. They may or may not combine sales for singles and albums. They may or may not include digital downloads and international sales. Nielsen SoundScan numbers are considered throughout the industry to be definitive.
BTW, I also thought that Kellie Pickler, Josh Gracin and Elliott Yamin would have shown up in the top 10 AI alumni, but they don't -- at least not yet. Sales figures are not static. They change daily, and with each new single and album release. So each new dataset should be viewed only as a snapshot, not a definitive statement of who has and has not had (or will or will not have) a successful career post-AI.