Metrics on Throttle Plugin

I'm interested in knowing how many times a particular key was throttled. I've been poking at this problem for the better part of a week now and the only thing I have been able to come up with is being able to determine if an event is throttled or not.

Am I missing something really obvious?

Thanks in advance!
-Andrew

You may need to use the https://www.elastic.co/guide/en/logstash/current/plugins-filters-metrics.html filter before the throttle one to get an idea of total through put, then again after to get a count at that point, then compare.