The rail planner app is not reliable and should not be used to plan. It only gets updates every few weeks.

The Trenitalia website is the right place to look. If the train appears there, then you can be pretty sure it will run.

If you want to book it, check on tickets.oebb.at. But there's no rush; Trenitalia don't have limited pass holder quotas.

Thanks so much, I was getting very confused so it’s good to hear the reasons behind things..! I was having a similar problem with the night train from Bari to Milan a few days after, but as far as I can tell that might be a more simple question of the tickets just not being available yet..? 

Yes-again someone who thinks too much that trains are like planes- waaaaaaaaaaaaaay too early now. The usual pre-sale period was always 2 month-stick to that as guideline. Plus that trenIT is aoften even later as that.

Hi again! I’ve been looking into this again and still a bit confused. The Bari-Milan night train is showing up to book on the trenitalia and italiarail websites (which don’t have an interrail pass option) but not the italiarail mobile site/app or oebb.at. If there is no pass holder quota I’m not sure why it’s like that or if we need to wait longer. Any advice would be welcome, thanks!

Italian night trains cannot be booked online through ÖBB. They can be booked online through the Interrail reservations portal:

I booked mine through Deutsche Bahn on the phone, and collected it from a ticket machine in Germany - which might also be an option for you if your trip brings you through Germany at some point before.

Italian night trains can also be booked by phone via Belgian railways. They will then send the reservations by email. Their phone number is not cheap though.

Via Italiarail it should also work, but via this link:

https://partners.italiarail.com/default?force_pass=true&aff=EURAIL