If it's a clean audit you want, we'd need to use some kind of machine fingerprint based on hardware configuration.
The real world problem is that sometimes UUID doesn't exist, and systems return all F's or all 0's meaning a collision is very likely if you stick purely to UUID.
Other than that, it really depends what you're talking about. Of course a ComputerName collision is very possible, especially if machines are cloned. In the case of UUID it depends how it's created. If it's pulled from the hardware, it depends whether the manufacturer has ensured that the UUID is actually unique and not some random string they have cobbled together.
Having said all this UUID isn't really the problem, when it's there. If it's not there, what do you use instead?
A GUID/UUID consists of 32 hexadecimal digits, same as an MD5 hash. SHA-1 uses 40.
So 75%? It depends on your resolution.
Perhaps a MD5 hash of ComputerName+(DOMAIN|WORKGROUP)+InstallDate is the answer...