Once I flew on 2 separate PNRs with *A carriers and had my luggage tagged all the way to the final destination.

When it was announced my first flight would be delayed significantly, I told an airline rep that I had an important business meeting that could not be rescheduled. She managed to put me on different route with another *A carrier and got me to the transit city in time before my flight to the final destination.

As a bonus, she booked me on a higher type of fare on the substitute flight (still in Y) which got me more miles. ^