Here are some articles that may be helpful
- Last Antivirus Updates Scan Date: In the "Scan and Repair Settings" Antivirus Updates is checked off and run on the client machine.
This refers to scanning against those items in this category:
This also explains some of this:
I'm curious about the last portion of his question that didn't get answered. I looked through the linked articles, but I didn't see anything regarding it. What is the difference between last full scan and last virus scan? Why are these dates so different for some machines?
I believe they are referring to two different things.
One is the vulscan scanning definitions of type 8, which is Antivirus related Patch and Compliance definitions.
The other scan is reported from the Antivirus client on the server back to the Inventory entry in the database.
This article should explain some of this.