TU Delft’s club profile says DSR-C was founded on 24 September 1918, then formally established as a rugby club on 21 October 1918. It says the club had 130 members right away, and calls it the oldest rugby club in the Netherlands. TU Delft club profile
The club’s about page gives the same sequence: founded on 24 September 1918, official establishment on 21 October 1918, 130 members immediately, oldest club in the country. DSR-C about page
The Rugby Nederland club page gives 21 October 1918 as the founding date. Rugby Nederland club page
Dutch Wikipedia dates the founding to 8 October 1918. This page does not treat one of those days as the founding date. Dutch Wikipedia
