1918: The different founding dates
TU Delft’s club profile says DSR-C was formally established on 21 October 1918 and immediately had 130 members.
TU Delft gives 24 September 1918 as the earlier founding date and describes DSR-C as the oldest rugby club in the Netherlands.
The club’s own account gives the same two dates and initial membership of 130. It also describes DSR-C as the country’s oldest rugby club.
The Rugby Nederland club page gives 21 October 1918 as the founding date.
Dutch Wikipedia gives a different date, 8 October 1918. These accounts agree on the year, but do not establish one undisputed founding day.