a train is missing from the planner

Probably it's not missing, but just not shown as to Rotterdam options are available departing later and arriving earlier (by IC direct). When travelling to Dordrecht the connection from the IC direct onto the train to Dordrecht is quite lengthy, so taking the direct IC is faster and thus shown in the planner.

The slower option you've put a question mark next to will be shown as it departs later than the IC direct, but arrives in Rotterdam before the next IC direct.

I am also concerning that people who make plans at NS may consider to cancel the train stopping at Duivendrecht, because little traveller step in… but that is simply because it is not in the time table.

Thank you for your explanation. But I am afraid it is not the case… You can see if you perform the same search in the planner.

It is, but not to Rotterdam as faster options are available. Even the Sprinter from Duivendrecht via Breukelen to Rotterdam is 5 minutes faster than the respective IC.

But plan a journey from Duivendrecht to Den Haag HS and the direct intercity does appear as an option.

At first I thought this as well, but the same goes for the journey to Dordrecht. There is a connection that departs later and arrives earlier, so why is the 7.16h train shown?

edit: Probably because with the 7.16h train it's a direct connection without any transfers.

Besides it is a bit slower. There are several pros of this train. There is WiFi, and it stops less than the Sprinter. Comparing to ICD, it cost less and no stepping out. Stepping out at Schiedam gives more opportunities for direct transfer for the next step travelling. Without listing it in the time table, it is difficult to compare and plan optimally. we should be able to see this option. 

Good morning Shengnan and welcome to the NS Community.

Why this specific train isn't shown for the advice between Duivendrecht and Rotterdam can be explained because the Sprinter option from 07:01 is faster (which in and of itself is also rather interesting).

Why it's not shown for a trip Schiphol - Rotterdam I cannot explain either, I've forwarded the question and hope to get an explanation, or perhaps even adjustment.

Thanks for your kind explanation, and it is good to know that the intercity may show again for travellers at Schiphol. However, between Duivendrecht and Rotterdam, I still question about the logic. Even the intercity + intercity +intercity is shown. Why would you like to skip the nice direct train, even better, with WiFi.