My (UK) diagnosis was an endurance test. It took 2 years of consultations, appointments and referrals to get a diagnosis. Of course, this is the NHS so everything non-life threatening takes longer but if there was no impact day to day there would be no motivation for the many hoops and consultations. Due to the nature of the beast, many who do suffer could drop out of such a marathon because, for example, their referral form had fallen underneath a filing cabinet due to a chaotic office and thus forgotten about by both sides (happened to me - called up because after 3 months after prodding by my mrs. She was going insane).

Overdiagnosis is almost a cliché. This might happen in some places. There are just as many that the diagnosis is painful and thorough.