It's called an estimate. They calculate what they've already found or what's historically been found then they can get a target number. Same as what a business does, they set goals based on their market. Like I know how much $$ I made last financial year from lures, now this financial year I set a target at say $3000, whether i hit it or not depends on how much work i do and how many people I can reach. Same thing for the gold hunters. Simple entrepreneur statistics.
All Ethan dose is complain how he needs more money,even tho they get a large amount of gold constantly,he's the biggest winger,he's extremely lucky to be associated with his boss who is a very talented gold miner,Ethan the negative Nancy's