I experienced that on many computer (>100 ) with Windows 7 that many computers don't report the complete list of software which are installed.
For example one computer is reporting only 220 Software entrys, but with all hotfixes there should be more than 700 items.
I think i found a solution
Just start the following on the affected client in the cmd (you can also deploy that command line)
and after some time the Computer will report a complete list of all items.
Perhaps with this command a windows wbem cache was renewed or something similar.