The quote doesn’t say that 30-40% of your gas is evaporating, it says that 30-40% of the hydrocarbon emissions are composed of products from evaporating gasoline, so obviously they are escaping the vehicle and not being 100% captured by the emissions system and recycled.
“My car can sit for a month or longer with no measurable loss of fuel.”
How do you know that? Have you measured it?
I am quite confident of no losses. If gasoline dissapating from a sitting vehicle was a common feature, I would, at my advanced age, be quite familiar with it - as would anyone owning and operating a vehicle in the last 100 years or so.
Post internet mumbo jumbo as you will, it amounts to nothing more.