All hearsay, but an IR examiner I flew with told me something similar a few years ago - that it was single-pilot equipped (so renewing his IR involved some blind faith in his abilities) and that the aircraft C of A was specific to him alone. Once he passed away, so too would the Certificate of Airworthiness.
He also told me stories of John flying through the alps in IMC, using his weather radar to plot his position relative to the mountains.
I have no idea whether any of this is true. My guess is, probably yes.
Beech Boy - who was the engineer?