Originally Posted by akl_cat

If you had used Airpoints to pay for even just a part of your flights, it would be marked as non-eligible for earning to another FFP.

When making a redemption your Airpoints number automatically get applied to a different field called FQTR. This prevents you from loading another FFP number into FQTV. Even if you tried to change it at check-in it won't work as your Airpoints in FQTR will always override.