Metric definition for sys_updated_by

I can't figure out why the metric does not create an instance if I am "watching" sys_updated_by or sys_mod_count. Has anyone else had a problem like that?

I have one metric definition that is a script calculation and another setup as a field value duration. I tried using sys_updated_by in the field value calculation and didn't "catch" anything. I also tried using sys_mod_count in the field value calculation and got no love.

That makes me wonder if these fields are really eligible for this kind activity. I looked at the "First Call Resolution" metric definition. It uses if (current.sys_mod_count == 0) { in the script and that seems to work no problem. That makes me wonder if I even have a clue how metrics really work. I have read and followed the wiki article

Metric Definition Support - ServiceNow Wiki

Ultimately, I am trying to get a count of tickets that the Service Desk folks "handle" without getting credit. We can run reports on sys_updated_by but that doesn't help if the ticket has been worked and closed by someone else. So, I'm thinking a metric would help me capture this information as it changes.

Any ideas? Any comments?