Year 1900 problem

The most common issue raised by the year 1900 problem regards people's ages.

In several countries, especially in Europe, a national identification number was introduced (often in the 1950s), including two-digit information about the birth year.

[1] When handling the year 2000 problem, measures were sometimes taken to avoid or rectify this: modifying the national identification number, for instance.

For example, year is recorded only with two digits in Bulgarian Uniform civil number; however, a solution was ready as early as the inception of the system in 1975: 20 was added to the month number for an individual born before 1900 and 40 for those born in or after 2000.

This also has the side effect that the WEEKDAY function reports incorrect values for the period Jan 01 1900 to Feb 28 1900.