If your Windows NT 4.0 server had implemented tip 0025, it should have maintained the DontDisplayLastUserName string value of 1 during the upgrade, even though the Value Name has been relocated to:

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\System

NOTE: The data type has been changed to a REG_DWORD.

When you upgrade, and select Terminal Server Services, the Tsoc.inf changes the value to 0.