IME the baggage allowance (first class, elite, whatever) reflects the segment onto which you first check baggage. For example, I've had BF awards connecting to HA. The HA segment was not in F. Outbound, full allowance, return, had to pay for a bag over 50lbs - even though ticketed BF on CO and elite.

I do wonder about itineraries which begin on an ERJ. That'd suck.