If the hoses just run from engine to heater core, no by-pass, then it doesn't matter which hose is connected to which heater core nipple.
My '94 is like that, heater core is the by-pass so coolant always flows thru the core, blend door inside controls heat in cab.
Heater core has no IN/OUT nipples, works exactly the same with flow traveling in either direction.
My grandfather taught me to swap hose connections on the heater core every two/three years, when you change the coolant.
This will hopefully push out any larger debris the way it came in and keep the core tubes open and working.
Same as back flushing the heater core.