'RTM', I've heard, also means, 'Release To Market' (as well as 'Release To Manufacturer'.)
I don't know whether that's true but I have seen
Windows 7 Ultimate RTM English Retail DVD ISO around.
You appear, anyway, to have 16385. Someone who has a retail version may be able to confirm whether this is
the build number?
Go to Start and type regedit in the search box. press Enter to open the Windows registry..then navigate to
HKEY_LOCAL_MACHINE\Software\M*crosoft\Windows NT\CurrentVersion (where * = i)
you'll find in the right panel the CurrentBuildNumber, CurrentVersion, BuildLab and BuildLabEx keys.
My BuildLabEx is 7600.1638.x86fre.win7_rtm.090713-1255.
I thought it was retail, too.
I've seen mention of 7600.
16399.x86fre.win7_gdr.090722-1835 or 7600.
16399.x64fre.win7_gdr.090722-1835
which, apparently, are mainly KB fixes which the rest of us would download in Updates.