Why are numbers of tracked visits changed retrospective?

Hi. I usually check the numbers of tracked visits and pageviews once per month for the past month and note them in a separate list. When I did so in the beginning of June, I noticed that the numbers for April, March and February had changed retrospective, compared with the numbers I noted previously. Some increased, some decreased, the total was different for this period. Older numbers were consistent and did not change, neither did this problem reappear in July/June. Does anybody know, why this happened? Thanks for your help!

Link to the GitHub issue you created: