Re: Another 20 (18) years...
But the problem appears that they *haven't* used a sliding window, they've used a fixed window. If they used a sliding window, the roll-over year would advance a year into the future each year, eg a 2-digit year always resolving to a 4-digit year between 50 years ago and 50 years' time.
if (year2 > (thisyear+50) MOD 100) year4=((thisyear DIV 100)-1)*100+year2
else year4=(thisyear DIV 100)*100+year2
// untested, fails on edge cases