Hi i will do my best to explain. An example - just say Peak has codes for his scents,which he does. Ok, he has a great birthday cake scent, that scent has a unique code which the manufacturer uses to produce that exact fragrance which you can purchase from them. Most places it is 25 pounds worth at a time. Now only peak can use that code unless they sell it or give permission for someone else to use it and order the fragrance.
Some codes are worth about $100 and some can be worth $1,000 it really depends on the scent and usage. Some people just give the code away as they are not using it, every case is different.
any amount of people can use the same code, the manufacturer does not care as they sell more fragrance.
Some fragrance houses do not work on a code system per say, like a few fragrance houses just sell scents based on the name alone, so you could buy their lilac and so can everyone else. Lerbuthmuth (wrong spelling sorry) is an example of this. They do have custom scents of course, but they also have a massive list of fragrances that anyone can purchase and you will find some candle supplies have the same fragrances all from Lerbuthmuth. I hope this helps and is not as clear as mustard!