I think this month is the first month that all (n-100) have been dropped and the same number added.
This has been happening since June 11, 2019. Maybe I misunderstood your post, because you've Merited this post.Slight misunderstanding of the question yes. What I meant was from the list of 100 selected the previous month, (n-100) are dropped and in their place all ( (n-100) <--> in this case = 34 ) who were not on the list the previous month are then added to the next month.
Every month the number of dropped users equals the number of added users, otherwise the total (100 DT1 users) would have changed.