Nearly fell out my seat when I seen so many systems showing up in the "Server : No Antivirus Software Report" with so many apparently missing it.
Then I drilled into the SQL for the report and noticed it is querying a table called dbo.tsysantivirus for AV products.
On running that I noticed one key record missing:
Symantec Endpoint Protection%
Given this is Symantec's core business AV it might be worth adding
The other one that stands out as missing is Microsoft Forefront Server Protection. I'm unsure how the client edition is identified however.
Hope this is of some help I will manually add them for now if I can.