Thank you very much for your detailed answer.
So frankly all kupeiny are designed to function as sleeping cars if needed?
Very interesting. I have been travelling a lot in Belarus and the baltic states, and I always wondered why all the cars had beds, even in day-trains.
While we are on the subject. While travelling from Klaipeda to Vilnius in Lithuania, I noticed they had 1st class kupeiny-type cars with open interior and seats, instead of 6-8 seat compartments.
I wonder if only LG have those?