I recently needed to check on when a particular member was added to a group with Category Moderator permissions.
Using the logs tab on the group in the GUI, I was easily able to see when the member was removed, but not when they were added; it looked as if they were never added.
Some playing around in the Data Explorer add-on confirmed there was no log entry of their addition.
What we’ve surmised is that on the Discourse page for creating a New Group, the user was set as the Owner at the time the Group was specified, so when the Group was created, they were “already” a member and there was no log entry made for their addition. (From the time the group was created until the addition of another member a year later, there were no additions to the group, which should otherwise be impossible.)
Bug Fix? / Feature Suggestion:
For accurate logging and forensics, I’d suggest that setting the Owner of a group be given a separate entry row in group_histories immediately after the group is created. This will ensure it shows up on the Logs tab of the group Manage page, which is otherwise confusing.
(It would also be nice if the group manage Logs tab showed the group creation date, but that might be more complex.)
Side note: I suspect the same is true of members added on the New Group page, but I have not confirmed that.