Found the information I think you need here are the AF rules:

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COMBINATION OF ALLOWANCES 06FEB2007
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1. PIECE CONCEPT/WEIGHT CONCEPT
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WHEN A PASSENGER FLIES WITH A CONNECTION (WITH OR WITHOUT A
STOPOVER) AND THAT ONE PART OF THE ROUTE IS UNDER WEIGHT
ALLOWANCE WHILE THE OTHER PART IS UNDER PIECE CONCEPT, THE
CALCULATION TO BE APPLIED IS AS FOLLOWS :
.
PIECE CONCEPT ALLOWANCE IS APPLIED ON THE ENTIRE TRAVEL IF
PASSENGER TRAVELS WITH AN AF OR SKYTEAM FLIGHT NUMBERS OR IF
TICKETS ARE JOINTLY ISSUED (EVEN WHERE THERE IS A CHANGE OF
AIRPORT IN PARIS).
.
NOTE : ON SOME IDENTIFIED TRAVELS (WITH AN IMPORTANT AMOUNT OF
PASSENGERS CONNECTING ON OTHER AIRLINES FLIGHTS), DELEGATIONS
MAY WAIVE THE GENERAL RULES (PC ALLOWANCE ON THE ENTIRE JOURNEY)
AND ASK THE STATION TO CHARGE ACCORDING TO THE BAGGAGE ALLOWANCE
SHOWN ON THE TICKET LEG BY LEG.
.
IN OTHER CASES : THE ALLOWANCE SHOWN ON EACH SEGMENT IS TO BE
APPLIED.
.
2. CHANGE OF WEIGHT CONCEPT ALLOWANCE
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WHEN A PASSENGER IS FLYING WITH A CONNECTION (WITH OR WITHOUT A
STOPOVER) UNDER WEIGHT SYSTEM ON THE ENTIRE TRIP, THE PASSENGER
RETAINS THE BENEFIT OF THE HIGHER BAGGAGE ALLOWANCE ON THE
ENTIRE ROUTE IF PASSENGER TRAVELS WITH AF OR SKYTEAM FLIGHT
NUMBERS OR IF TICKETS ARE JOINTLY ISSUED (EVEN WHERE THERE IS A
CHANGE OF AIRPORT IN PARIS.
.
IN OTHER CASES : THE SPECIFIC BAGGAGE ALLOWANCE OF EACH SEGMENT
IS TO BE APPLIED.