Total assignee count over time?

We’d like to show a productivity metric (like “Issues resolved count” for all projects) over time, but normalized by the total number of Jira users/assignees. It looks like the Assignee member isn’t related to a time dimension, so I get a constant count of assignees over time.

Is there a way to define this time dimension for Assignees? Users don’t log their work, so “Logged By” doesn’t help either.

Screenshot 2022-09-23 111834

This is not a proposed solution, I only wanted to who how I defined the AssigneeCount measure.

Screenshot 2022-09-23 111733