Many moons ago, my colleague B and I worked on and supported a patient registration form management system for a health-care group.
There was one tech-support case that had us stumped. An older gent in his 70s was admitted on his birthday, and his calculated age was off by one. We were stumped.
Until I had a brainwave. He was born during the Japanese occupation of Singapore. Perhaps…
It was a Java application, using Joda-Time for date and time manipulation. A quick spelunk of the code confirmed my suspicion. Singapore’s timezone was GMT+9 during the occupation (in line with Tokyo’s). He was born shortly before midnight, so it all matches up.
Talk about your edge cases.