From memory, I thought it was a couple of US releases that don't work on the supergrafx, even when its region modded.. Somebody who knows for sure feel free to chime in.
Also, some info about pin 29: on the Duo R/RXs, pin 29 is NC. It doesn't go anywhere, so there is no need to life it from the PCB like is usually suggested. You can just solder your ground wire to it as-is. I'm going to verify this on my coregrafx as well, but I suspect its the same on all models.