I now know much more about Japanese dating systems than I did before this challenge! At first I thought the challenge answer was incorrect as wouldn't 01-01-1998 be still year one from an era starting 01-15-1997 since it is still inside of the first year of the era? Research determined the challenge answer is correct and the year designation for the Wareki format is based on the Gregorian calendar year. So for an era starting 12-31-2030 with an era designation of Y, 01-01-2031 would translate to Y020101! Fun fact for the next time I get to play Cliff Clavin at the bar.
After peeking at a couple of my favorite contributors' submissions, I think I may have missed some part of the instructions. My solution will detect if there is a date (looking for a "-") being input, and diverge from there... no UI tools.
Great challenge! I couldn't stop myself from putting extra bits on to make it more Dynamic!
And the Interface: