According to our codebase, it's mythical. An expiry date was set one year in the future, and the code used the obviously correct solution:
my @expiry_date = ($current_year + 1, $current_month, $current_day);
This date eventually makes it's way into a big, ugly C# app that doesn't like mythical dates or providing useful error messages. According to our source control, that line has been there for 6 years. According to our issue tracker, it caused a problem 4 years ago that couldn't be replicated, and was resolved after 2 days by re-running the script. The problem happened again recently...