Incidentally my fastest 50 miles was done somewhere on a 100 mile TT but my 50 mile TT best remains the one I did in a 50 mile TT.
My fastest 50 miles was done somewhere on a (sadly now annulled) 100 mile TT and my fastest 10 miles was done somewhere on a 50 mile TT. Thinking about it, my fastest 25 miles may have been done on that 100 too.
Back on topic, arguments about records for stated years that start on January 1st rather than say Feb 9th or Jun 16th are IMO very petty indeed. It reminds me of whichever hour record contender it was who spent his twilight years doing hour records at sea level, on a traditional bike, with one leg etc etc. As Mcshroom says, both Kurt and Steve still have to ride on every day of the year, no matter which one they use as a start date.
Equally petty though is the argument that they aren't breaking Tommy's record, just the HAMR. Whatever the UMCA say, everyone knows that the furthest anyone has ridden in a year is 75,065 miles and that it was Tommy Godwin wot did it.