Generally if its all on one ticket on most airlines the PIECE concept will prevail. This is generally the way it has been done for the last 20 years or so on almost all carriers. That being said, I have seen a few Euro carriers try to get around this with 24 hour rules as some state. Generally speaking however I have never seen a ticket (and I referring here to trips all issued on one ticket here) that flips between a weight and piece concept, the generally will say 2 PCS for all segments.