As long as the journey is added as one train without a connection then only the departure day will be used.

It is the same train so just add it like one train in the Railplanner. You can do that manually if you can't find the train. However, if you filter on "night train" in the Railplanner, you should see the direct train from Berlin to Stockholm. 

The reason for this is that some couchettes only run Berlin-Malmö and some seating carriages only run Malmö-Stockholm. 

Hello

Could you tell me how you get your reservation for the Berlin-Stockholm ? On their website, they said : we have to write an email. Any other option to book a couchette compartment ?

tanks for your help,

Karine

@karinka You must contact Snälltåget customer service to make an Interrail reservation. 

Thanks @AnnaB do you know if there is other nightrain between Stockholm and Berlin ?

There's also the SJ night train. Book on sj.se.

@karinka The SJ Euronight is st the moment only bookable until the beginning of April. Reservations for the summer should be available in the coming weeks.

Thanks ! I will check :)