Billboard is changing the way they list catalog records for the Billboard 200. Previously, only albums released in the last 18 months were eligible, and after that date, regardless of sales, the album could be the #1 seller, but not reported on Billboard 200.
This is changing, in large part, due to two events this year: the re-release of the Beatles catalog albums and the soaring sales of Michael's music, especially Number Ones.
Here is a good explanation of the change by Reuters.
Michael is also on his way to be the top selling artist for the year, second to Taylor Swift. What can we do about that?