What I'm getting at is: I'm an egotistical fool and I may have just been proven wrong. I just want to make sure that I really am wrong before stomping my feet and going to a corner to pout... :D
Brady mentioned the two factors being the caffeine content of the bean and the extraction method, but which one carries more weight? Would a robusta espresso shot have more caffeine than an arabica blend drip coffee? Just curious.
But further than this, you should accept not knowing what thing during extraction could change the concentration of caffeine.
Hope this helps. Looking for helpful external references as we speak.