Multislot has nothing to do with credit display. Maybe some individual games are different in their settings. But, I have all bios and I'm telling you JP/EU is credit on the right and shared, US is both sides.
Same can be observed with a unibios by changing the region. The reason is, they were set up to run off of cabs with one coin chute. All US cabs have independent coin chutes and that's why credit displays on both sides.