I don't have official number, but join the "a lot" vote.
I am not sure if you'll find a good correlation to developer or area experience, at least by my personal experience people offload memorizing of stuff to Google search
I am not sure if you'll find a good correlation to developer or area experience, at least by my personal experience people offload memorizing of stuff to Google search
But there are - as an aside - very real health benefits to having memorised the work. You're making less decisions (ie "what to google" and "is this useful"), which means you have way more willpower and energy for your daily life. Which is, of course, largely anecdotal but I think goes a long way to explaining traditional developer body types vs those in, say, finance.
(It's not like finance people are "less academic" than developers, for example).