I've finally gotten around to digging into some reports. I am seeing major discrepancies in time stamps. A computer can be listed as Last Checked in in June of this year yet will state the Agent Upgraded yesterday.

What are the differences between Last Contact, Last Boot and Agent Upgraded?

One would think that if the agent was upgraded, it had to have some sort of contact with the server to realize it needed to e upgraded, thus the other time stamps would update and reflect. 

Examples: