https://otc-cta.gc.ca/eng/publicatio...pretation-note says:
Baggage rules of the MSC are applicable from the point of "baggage check-in" until the next stopover, or the next point of baggage collection. Each time baggage is re-checked by the passenger, the MSC is once again defined and its baggage rules are applied. The baggage rules of the new MSC may be the same or different than the previous MSC. There is potential for several different MSCs to be included in a passenger’s interline itinerary if it involves multiple flights and stops.