We have had something like that, we have 4 clubs, one of which is not taken by our main sensei. They joined us from another organisation and just train under our name. However all the black belts grade together. On this occasion two of our students were taking Shodan, as were two of theirs. Our 2 completely outshone them, they are fantastic anyway but up against the other 2 they were in a different league. Its a shame as they let themselves down and their instructors.