My recollection is primary J service came out of the forward galley (from many 945/940 DFW-SCL flights). Possibly breakfast service in the morning came from the mid galley (I’m usually only awake at the clean up phase of breakfast). I never recall any “split” service where front and rear J cabins were serviced from separate galleys for the same service. I recall them making coffee as fast as they could in the mid galley to feed further back into coach.