FYI - The FAA is checking up and trying to get all the registration details correct. Although not urgent now, it may be come very important soon, certainly AOPA thinks so. There are a lot of 337's on the FAA question list if you go and look.
You might want to check the FAA's database
(
http://registry.faa.gov/aircraftinquiry/defimgUN.asp ) to make sure that your aircraft is properly registered.
Regards - Dave