This sort of info lack integrity for various reasons -- selling something being underlying reason. But, in the ight environment and such you should get close to what comes advertised... it's most likely an optimal outcome, and outlie outcome or just lying, though.. lol... it'll always be a number seen through rose-colored glasses.
Your regional DLI for the time of year will be single greatest factor to yield outside. There are maps with this info of avarege DLI per month for your region.. .google will help you find them.
Less than 40-ish and higher will mean some loss of potential yield by comparison. Anything above 22ish should at minimum allow the plant to form decent colas. Feeding properly is also needed, of course.. and temps/RH are important too. But, these factors are more about avoiding problems that reduce yield than forcing anything to happen. it isn't foie gras :P