BA flight number, BA metal.
Note, we now need to specifically take care of OpenSkies (EC) too. The 4 qualifying flights could be EC flights on EC metal - that would meet the requirment too.
Plus it should also make clear that BA subsidiary and franchise partner flights count as BA metal.
And if it could reassure people that flights that are subbed out to be operated by a third party / wet-lease etc, but are BA/sub/franchise flights count then that would be great too!