I was a bit confused at first. I have always expected to have an extra bag on OW itineraries. Then I remembered that OW also has an extra bag benefit for OWS and OWE. So when flying mixed itineraries all on OW, it's the OW benefit that is applied, not the Finnair one. If flying mixed OW + other airline then IATA most significant carrier rules apply. If flying codeshare on entirely non-OW then you're just s*** out of luck.