WSUS console not showing all computers

I have a Windows 2008 server which is part supported by another company who also installed it.

Since it was installed the WSUS console on the server has never showed all clients. At the moment it is only showing 15 and there are more than 100 machines on the system. They did try reinstalling WSUS but it still is not shoing all clients.

They have said this is normal for WSUS and it is unreliable. Is this normal, or is this a known issue with a fix or should I be harrasing them to get it working correctly?
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Neil RussellTechnical Development LeadCommented:
Are your PC's cloned from a single image?

if so then you HAVE to clear the WSUS settings in the image Prior to deployment of the image.

For the ones you have already deployed you can run the following script. Save as a .cmd file and run on each client.

rem Fixes problem with client machines not showing up on the server due to imaging method  
reg delete HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate /v AccountDomainSid /f 
reg delete HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate /v PingID /f 
reg delete HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate /v SusClientId /f 
@echo Triggering detection after resetting WSUS client identity 
net stop wuauserv 
net start wuauserv 
wuauclt /resetauthorization /detectnow

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Also,  Check the name of the client computer group that WSUS is using and make sure all your clients are part of that OU.  
A very basic thing, does your GPO with the wsus settings target all clients?

You might find some useful information for troubleshooting in this technet article:
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Windows Server 2008

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