can i call the sysVariable without running acad..?
Nope...
In this case you've to check the 'Release' field in the registry:
HKEY_LOCAL_MACHINE\SOFTWARE\Autodesk\AutoCAD\R16.2\ACAD-4001:409
HKEY_LOCAL_MACHINE\SOFTWARE\Autodesk\AutoCAD\R16.1\ACAD-301:409
HKEY_LOCAL_MACHINE\SOFTWARE\Autodesk\AutoCAD\R16.0\ACAD-201:409
HKEY_LOCAL_MACHINE\SOFTWARE\Autodesk\AutoCAD\R15.0\ACAD-1:409
Note:
The release number can be at different positions of the release number block and also have different values:
2k6 SP1 = 16.2.77.0
2k5 SP1 = 16.1.84.0
2k4 SP1a = 16.0.0.124
2k2 SP1 = 15.0.6.044