Bob Ogden in the reference book ‘Aviation Museums and Collections of Mainland Europe’ (Air Britain 2006),  entry for this aircraft is:

Nord 1002 Pingouin II, construction number 163.  Previous identities: 163 (military serial, but no Air Force noted), HB-OAR, (D-EHUX ntu), HB-OAR, D-EOAR, (D-EACS ntu), ‘D-EFAG’ false identity.  Status code PVX: public view with a false identity. 

Adds little, but with the information that some registrations were ntu (not taken up), the question in the opening post may well be answered.