I read the same thing on my state's licensing board's website. I was searching for as much information as I could find and came across the page that described the process of how the board assesses which complaints are worthy of investigating. I don't know if I can find that link right now. In there it was said that about 2/3 of complaints don't get investigated because they lack evidence and for other reasons. After I filed my complaint I received the response from the board explaining that it'd take them some time to review it to decide if it warrants investigation. So, no, they definitely don't investigate every complaint. I can believe that most of them get dismissed as not credible. Many people have no idea how to write official documents in order to be taken seriously, so..