With SWUs, I'd often use a single certificate to upgrade up to three AA flights between Europe and South America, for example, CDG-MIA-BSB or MAD-JFK-MIA-BSB.

When using Business Extra Upgrade Certificates (BXP3), as long as my underlying flight is in the appropriate booking class, do I correctly understand that TWO certificates would be required for such itineraries? Or, in practice, could one BXP3 be used for the entire one-way ticketed routing?