Thanks! Cool to see how steady signups have been outside of those anomalous events!
I think your ???-peak on july 19th 2013 is due nova.gs and online-go users merging into the same database, since the merge happened exactly 3 months later on october 19th (not the october 3rd, i’m not sure what that peak is, but i guess it too has something to do with the merge.)
In general a lot of things about old OGS are broken. registration_date field for pre-merge accounts can be wrong. I only recently discovered that there’re accounts with games played before their registration date.
One idea is to look at old accounts and if they have a game older than registration then count the date of the first game as registration date. In that case big portion of 19 Jul peak disappears.