I came across this example from SU:

You have a ticket Oslo-Moscow-Delhi-Kathmandu booked on the following flights:

SU212 Oslo-Moscow
SU535 Moscow-Delhi
9W264 Delhi-Kathmandu

SU212 and SU535 are operated by Aeroflot.
9W264 is operated by Jet Airways.
Aeroflot uses the piece concept.
Jet Airways uses the weight concept; 20 kg.

First of all, MSC in this itinerary is Aeroflot, as flight SU535 crosses two IATA areas. Therefore the piece concept applies.
However, with this particulary itinerary there is another challenge; which piece concept will apply?
Aeroflots rule is 1 piece, but on tickets to Delhi the airline offers 2 pieces (the "double baggage" offer).
It is therefore important to understand that this ticket is a ticket to Kathmandu, not to Delhi. Delhi is only a transfer point.

Conclusion: 1 piece max 23 kg applies for the whole routing Oslo-Moscow-Delhi-Kathmandu.

By the same token, my flight will have allowance of one piece, 23kg.