Have seen errors in pipeline where associated data added to an alarm configuration gets corrupted in the namespace and does not reach the pipeline.
The pipeline does not check the tag configuration of the the source tag and verify everything made it through to the event object.
You also need to know what keys yourself to be able to use them on the event object. If you print out the event object all you get are the basic keys no details about associated data at all. So if you created an associated data called "alarmGroup" on your alarm, you need to know that to reference it in the pipeline with event["alarmGroup"] because there's not way to get keys from event object in pipeline.
The pipeline also does not care if "alarmGroup" did not make it to the pipeline. If you referenced a key that doesn't exist in the event object, it will just return None with no error.