I’m thinking about using my pass to board the Vienna to Kiev sleeper, but I might prefer to do so from Budapest rather than Vienna.
Of course Ukraine isn’t in the Interrail pass area, but you can use a pass to cover the section up to the border, which is really useful. This isn’t something I found out myself, it’s from this helpful blog: https://railguideeurope.com/nightjet-eurail/
Anyway, to cut to the chase, the price from Vienna, for two passholders sharing a compartment, bought at oebb.at, is €114. However, this can only be bought from Vienna (not from any other station en-route) and the ticket can only be collected in person within Austria (so I would probably have to do the journey west-east, in order to have been to Austria first).
To buy from or to Budapest, the only option is to go with an agency like Polrail, which doesn’t count any Interrail discount, and charges a whopping 1220zł (€270), plus whatever postage of the physical ticket costs to where you live (unless you collect in person in Poland).
Given a choice like that, it seems a pretty easy decision to make to buy the whole journey and save €156, but not use the Vienna-Budapest bit. But would I get away with it when boarding at Budapest? Or would I be deemed to have forfeited the compartment and invalidated my ticket?