For instance it is said that Ilford makes Fuji chromogenic 400 film. Well if it does make that other maker's film does it use Fuji backing paper or its own
The machine that packs the film proably uses some of the little bars and dots on the paper to locate it in the machine, so if they are packing film thay would have to use paper made with those markings in mind.
If they make a given film for Fuji, I would guess it would be more likely for them to ship the raw rolls, and let Fuji pack them on their own machines. On the other hand if they pack film for Maco, they may receive the bulk rolls and just pack it with their own paper. for example, I have noticed Maco advertising a version of CR200 in 120 in packaging like the rollei 25 and friends.. IF Illford packs that they would receive the film in bulk, as they do not make any colour film themselves.