When travelling internationally in Europe by train, it pays off to consider with which railroad operator you book your ticket.
For the the same ticket, more than a month in advance, both DB and NS were compared.
Even though one would be travelling with exactly the same trains, there is a €53 price difference between the operators. In other words, a DB traveller could save 62% by booking via the NS for this particular trip.
(Screenshots date: 29 July — tickets date: 3 September — tickets type: 1 adult, no reduction, second class from Venlo (NL) to Darmstadt (D).)