"Oh well. That's an hour in a Dr400 I've wasted every couple of years, then."
Are you thinking of your "Biennial hour with an Instructor"?
At least 75% of my hours are DR1050, but my "hour" is always a check-out on a flying school rental. My last tailwheel check was 1965.
With no instructor involvement, I flew home a Bolkow Junior we bought a year ago. Should a sign-off in my log book by an instructor who'd never flown that model been made? Few instructors are available and current in rarer aircraft.