You recall incorrectly. Windows NT kernels have been able to unlink open files right from the get-go, at the start of the 1990s. They had to be, in order to support the POSIX subsystem.

When files are manipulated through the Win32 subsystem they are (normally) opened in "deny delete" mode (i.e. without passing FILE_SHARE_DELETE to CreateFile and thence to NtCreateFile). But that's Win32 programs and language runtime libraries explicitly setting the sharing mode flags that they like, not an inability of the Windows NT kernel that is below the Win32 subsystem, nor even an inability of the Win32 subsystem itself.

* https://msdn.microsoft.com/en-gb/library/windows/desktop/aa3...