Yeah I realized this about the network board. They are per region and if it's not properly emulated then that's why I guess. Needs those eeprom/flash dumps from the network board ideally.
I know racing jam doesn't check for CRC (I don't think SS1 does either actually) so I assumed this would be fine. Apparently not!
I've since tested the jap timekeeper dump anyway and it works so I guess at the very least that can be included in the next update.