I'm keeping track of some statistics on 3 beta sites I participate on, by listing bi-weekly the site's statistics from Area 51. I've been doing this for about 4 years but today I noticed that for the first time the 'total users' count of a site went down. This happened on all 3 sites. For example Martial Arts had 5479 users on January 10th, and today it's 5397 users. For interested people, the historic statistics are in this Sustainability SE Meta post, this Martial Arts SE meta post and this Personal Productivity SE post
Has there been a cleanup of user accounts again (this post says it's not done anymore)? Or has there been a change in how this number is calculated?