Yesterday I discovered a bug in wikistats which affects our editor counts for the last 2 years.
Wikistats does flag users as ‘anonymous’ based on pattern recognition, rather than relying on the <ip> tag. Reason: many anons with other pattern than just 4 numeric triplets (e.g. 123-12-123-12.adsl.xs4all.nl) ended up in the <username> tag in early years). To my dismay I realized yesterday this recognition code was never adapted for ipv6 addresses. Hence those anonymous ipv6 addresses were counted as normal registered users in many reports. Especially for the last 12 month this visibly affected our totals for active editors (5+ edits a month), hardly so for very active editors (100+ edits a month).
Today I fixed this for our report on total unique (aka deduplicated) registered users for all Wikimedia wikis combined. The chart below show how much counts were lowered because of this. Other reports will be fixed after June’s dump processing cycle.
My sincere apologies for any confusion or inconvenience caused by this.
Update: Here is a second chart which shows the effect on our active editors in absolute terms. For very active editors the difference is negligible and can not be shown in such a plot.
(for comparison here is the old version of the report)