When you enter a year using two digits, the corresponding four digit value is determined by a setting in Collabora Office - PreferencesTools - Options - Collabora Office - General. For example, if 1935 is set as the lower limiting value and you enter 34 as a date value, then the result is 2034 instead of 1934.
The pre-set limit value will be saved for each document.
In Collabora Office, years are indicated by four digits, so that the difference between 1/1/99 and 1/1/01 is two years. This Year (two digits) setting allows the user to define the years in which two-digit dates are added to 2000. To illustrate, if you specify a date of 1/1/30 or later, the entry "1/1/20" is recognized as 1/1/2020 instead of 1/1/1920.