Most Reichsbahn passenger waggons had electric heaters in 1939 and earlier, 1 small in every cabin.
Unsure if any Reichsbahn still heated with coal or so. Maybe in some cattle waggons, that were
used in 44-45 for evacuation purposes, or for KZ and war prisoner transports.
Reichsbahn had more than a dozen different passenger waggon types. For example the ones you mentioned, passage on one side,
cabins on other side. Also there were waggons with passage in middle and cabins left and right.
Or Waggons with passage in middle, and open spaced seat groups left and right.
There were also waggon models with 2 levels, they were used for 2nd and 3rd class mostly (cheaper tickets, less space and comfort for the traveller)
Some waggon models had doors to exit and enter the train from the station platform, while other models had only exit
and entrance on top and back of the waggon - you could go from it only into the waggon infront or behind.
Hope you get what i mean.
To make it short, there was alot of different waggon models.