Source: Gary Leff - View from the Wing
American AAdvantage gives out 8 confirmed upgrades per year valid on any American flight (both domestic and international) to their 100,000 mile ‘Executive Platinum’ members. They also give out these certificates at million-mile thresholds.
The rules of the certificates are that they have to be used to travel by the expiration date on the certificate.
But it wasn’t actually enforced that way. If you had any certificates that would be valid into the future, you could use your earlier expiring upgrades, because the system was set up to pull the closest-to-expire upgrade certificate first.
This meant that it was possible ...