It is possible to refuse to load the egr(1) extension for simultano/corona, MAME would then give an error like this:

Software 'egr' is incompatible with system 'simultano'

But I'd like to know first if it's a MAME bug or that egr isn't detected on the real chesscomputer either. Do you have an EPROM programmer and a spare 32KB EPROM to try it?

If it is an emulation bug, I shouldn't add a filter on the softwarelist. I did try a few things already, but it still didn't detect egr1.