Hi Dale,

We had a similar need for a vendor which bills us per ticket and works out of our instance. We ended up using the solution that Mcgasey300 put forward in his post on this thread. I think you could take his idea and expand it. The synopsis is that he created two list collector fields on the task table which are updated anytime the assignment group or assigned to changes. This allows you to target those two list collectors in reporting to identify what all groups or individuals were assigned to work a record. 

For you, I would modify this solution a bit and have the business rule add anyone who performs one of the actions you outlined. You may end up using multiple list collectors for each of the actions so you can report on which action each person took but that wouldn't be too hard to read through on a report.