I have two separate tickets with BA, one in ET OSL-LHR-OSL and the other one is CW LHR-JFK-LHR.

On OSL-LHR-JFK I will only check in one piece of baggage. But on the return maybe I will need to check in 2 pieces of baggage (NYC shopping... ). CW from LHR-JFK allows 3 pieces, so that is no problem. But ET from LHR-OSL is only allowing 1 piece. Since BA will probably be able to check my baggage to my final destination from JFK, how will they handle the 2 pieces when I'm checking in at JFK?

Just wondered if I need to buy 1 piece of excess baggage on LHR-OSL on ba.com, or should I just assume that a CW-ticket and the BAEC Silver will "solve" this issue at JFK?