How such a “professional” was entrusted with programming a system with real-world monetary
consequences is a mystery.
I wrote a calendar program in high school that accounted for leap days, the lack of leap days in years divisible by 100 (unless the year is also divisible by 400), and the 1752 switch in England and its colonies from the Julian to the Gregorian calendar. (That last bit was accomplished by simply refusing to print a calendar for years before 1753).
This was so long ago that I typed out the program on a terminal where the display was a roll of paper on a teletype.