It appears that each orderer keeps blocks of each channel, would this mean that the orderer.c will see transactions on the A-B channel, and so will orderer.a see transactions on the B-C channel?  If it does, to prevent orderer.c from reading data on the A-B channel, each org would have to run multiple orderers, and so the A-B network will include only orderers of org-A and org-B.  Or you can put sensitive data in private collections that only org-A and org-B can read.