>> "- IsGenuineEx() returns TA_E_ACTIVATE.- Based on the documentation of IsGenuineEx() I was expecting the return to be TA_E_INET."
Don't disable network adapters. Disabling network adapters alone won't cause IsGenuineEx() to return TA_E_ACTIVATE, however, it will change the fuzzy fingerprint in TA 3.x. So something else is also changing.
In TA 4.x we've fixed the interesting user behavior where customers disable network adapters.
To test "no internet", unplug the Ethernet cable or disconnect from the Wifi network. Don't disable network adapters.
>> "(I assume the utility uses IsGenuineEx() with non-zero values for nDaysBetweenChecks and nGraceDaysOnInetErr)."
No, it uses IsActivated().