Hi koolfaraz,
Based on my research, It seems that the Operating System Version means Windows operating system version (such as, 6.1.7600, 6.1.7601, 6.2.9200) and for non-Windows operating systems, it would be null.
Also, Operating System Build may be such as, 9200, 7601 for Windows operating systems.
In addition, we can run systeminfo from a command prompt on Windows OS to check that.
Related reference:
TechNet Thread: in NPS 2008 R2 , in NPS network policy operating system
condition , how we should point to windows 7 operating system ?
TechNet Thread: NAP Conditions - Operating System
Hope this helps.
Jeremy Wu
TechNet Community Support
