(US based) I'm a human snail mail spam filter... It is possible for me to have physically received the mail, but promptly tossed it because the volume of ads and spam dwarfs actual mail. I've also found unopened mail in my trash by accident because it was tucked inside of supermarket flyers/etc that were tossed.

So, its quite likely that both cases are true, if you consider that there is a difference between physical reception of the mail and actual knowledge of what was sent.

I'm not really sure what the solution is, except maybe to pass more laws that keep the spammers from trying to make their mail look like official business (which is common because it increases the number of people that open the mail).