The Victor crew came across an article* that seemed very interesting regarding the amounts of caffeine we are actually consuming is based on several factors.
One factor is what type of coffee you are brewing. Caffeine is actually a natural pesticide so it will vary in the beans dependent on where they are grown. If they are grown in regions where there are a lot of insects, the beans will adapt and produce more caffeine.
Another factor is the size you grind your coffee. The smaller the grounds, the more surface area they have. Different brewing methods use different sizes. Cold brew uses a larger grind while espresso uses a fine grind.
Water temperature can factor in as well. The higher the temperature the higher the extraction is. Cold brew would only extract about 75% of the coffee.
Brewing style matters as well. You completely cover the grounds with immersion brewing where you leave the grounds sitting as opposed to simple pour over.