With its 955.122 movement it should be a 980.021L rather than a 980.021n. If it had the 955.114 movement it would be an N.
The L models used the 955.122 movement when serviced by Tag which replaced the ESA 963 series movements. Tag usually installed the smaller screw down crowns at the same time which this appears to have already.
The L models had a slightly more domed caseback to clear the taller movements. An N caseback would not leave enough room.
Thanks,
Justin
TAG1000Diver.com