Aside from on field and training kit, which is handled by the clubs and has strict standards on what can and can't be produced under it, all the NRL's merchandise is licensed out centrally by the NRL. It's the standard practice in the industry these days.
They license those contracts out under a handful of categories, but the vast majority of NRL merch is produced by two or three companies at any one time. It's why most of the merch is just recoloured versions of the exact same stuff. The nuts and bolts of it is that it doesn't get made unless the companies that hold those merch licenses agree to it.
The Broncos and NSWRL actually had massive spats about this stuff in the early days, as the Broncos approved the production of a whole bunch of products without the NSWRL's approval. That's why so much of that early Broncos merch, like the Alfie Langer action figure and Broncos Cheese Rings, is so random and rare.
Take a look at this relic lol-
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