There are full reciprocity between CO, NW and KL, including codeshares. However, they have different upgrade seat inventories. You can only upgrade if the inventory on the flight you booked is available. For example, CO9 and NW7009 are codeshares, upgrade is available on CO9, but not on NW7009; you can only upgrade if you hold coach ticket on CO9, not if you are on NW7009, even though they are actually the same flight.