Wrong. Under Dutch law, old and new (i.e. old civil code, which applies to this case, and the post-1992 new civil code), there is such a thing as a general obligation of good faith. That means that the court can decide that in certain extreme conditions it would be unequitable to apply the limitations period. (To be precise, it would be lacking in good faith for the defendant to rely on this argument.) The question is whether this situation qualifies.
In the past, the Supreme Court has allowed such "equitable tolling", as it would be called in the US, in a few cases. For example, it is a bit harsh to apply the limitations period to damage caused by an unlawful government decision if such a case cannot be brought in the first place until the administrative courts have annulled said decision. Similarly, the starting date of the limitations period should reasonably be moved up in cases where the damage is hidden. But in this case the problem isn't that the plaintiffs couldn't bring the case, but that for whatever reason they didn't.
Nevertheless, the court lists a number of factors that might reasonably suggest that the usual reasons for having a limitation period do not apply here very much. For example, the state accepts the plaintiff's version of events, so there is no major dispute as to facts and no need for serious quantities of evidence. And for some reason that I won't claim to comprehend the State gets blamed for sitting back and doing nothing all these years. Then the State's continued activity with World War II debts gets dragged into it to show that the State "has not yet closed the book on this era". Etc. All of which is well and good, but none of which explains why this situation is just as extreme as the ones already approved by the Supreme Court, which seems to me to be the relevant question.
The plaintiffs actually made a second argument, which might have gone a long way towards making the court's case. They argued that equitable tolling is required here because applying a limitations period would violate fundamental human rights, etc. This argument is a little wobbly, because the ECHR does not directly apply here both because of time and because of place, but in general terms it might work. If the case concerns something as serious as a war crime, a limitations period might not be appropriate. However, such a decision would require an explanation as to why the court should claim the right to make that decision itself, rather than basing its decision on a statute or treaty. (None being available.)
Moreover, it is a bit of a strange argument, since it puts the cart before the horse. After all, it involves basing the court's willingness to investigate a case on the seriousness of that case. That is fine here, since there is no material dispute as to the facts, but if that were different, the result would be that the court is basing its decision regarding the limitations period only on the facts as stated by the plaintiff. And that can't possibly be good policy, regardless of whether you would allow the court to later change its mind again.
And just as icing on the cake, the court decides - because it feels like it - that the wives of the victims and the plaintiff no. 8 (who was an actual victim) may sue, but that the limitations period stays in place for the other plaintiffs, because they weren't sufficiently closely connected to the events. Yet more mixing up of merits and limitations...