Hi Dominik,
I repeat,
The table CVERScontain System component version information in ABAP system.
The table BC_COMPVERS contain System component version information in JAVA system.
It’s very strange that in your ABAP system don’t contain any data in table CVERS.
There are many way to find out the sap version (Release).But from OS level, Reading data from the above table are most relevant.
All the best !! 
Regards, Praveen