It is possible to find the name for a week day if you know
The very first week day you can find is January the 1st
Year 1000, which was a monday.
Until the 4th of October 1582 it is the Julian calendar,
which is the base for the calculations. After that date
it is the Gregorian calendar which is in use.
Not all countries, which were using the Julian calendar, were
changing to the Gregorian one at the same time.
The Roman Catholic countries were changing in 1582.
The Lutheran countries (including Denmark and Norway) were changing
United Kingsom changed in 1752, Sweden in 1753. Russia changed
in 1918 and Greece in 1924!