Okay, I have done this before, but time to retell.
Some years back there was a documentary series on the BBC about perfume. The history of Guerlain was one showing the original notebooks from Jacques Guerlain. One episode was about celeb perfumes, so the company approaches a singer, actress etc and offers a deal. Depends on how big you are, how much you will get. The company hires a perfume making company, not your Chanel's etc, but there are perfume companies who just make endless different formulas and sell on. It showed a lab and sorry cannot remember who she was but not famous now sniffing vials with numbers and asked which one she liked. She picked one and that was it, this was going to be her perfume and marketed either with her name or one the company picked. Depending on how well it sells, they might release a flanker smells like the original one but different name. Think Britney Spears and her endless perfumes. Some remain big sellers, others just disappear. And that is how it is done. Of course the celeb will insist that they wear their perfume all the time which is Bullsh*t.
One of the most famous was way back in the early 00s Nicole Kidman was hired as the face of Chanel no5 massive TV ads etc. She was on an American talk show and asked what her favourite perfume and what she wore? She said it was, and I totally forget the full name, but it was rose by the perfume company?