For through journeys where the passenger travels partly on first or Business class and partly on economy class, the free baggage allowance for each portion of travel shall be granted according to each purchased ticket class.
Where a passenger who has paid the First or Business class fare travels on Economy class, the free baggage allowance shall be given based on that for the First or Business class service respectively.
so from what i'm understanding, if you have a segment in economy, even if you're booked in first for your first segment, your econ segment would still be based on econ baggage limit... that is
p.s. who would be stupid enough to pay for first/business class fares and travel on econ....