All debt falls off your credit report after 7 years.

As an American (though not the OP), I think it's fair to start with the interpretation that any American medical bill is an admin mistake until proven otherwise. Until each line item has gone through a few rounds of verification, it's very likely that it contains at least one error.

I always check the bill, in the particular the medical coding - I've very very very rarely seen one that was coded correctly.

When I complain they offer me a "courtesy credit". Or I don't complain and just don't pay since if they can't be bothered to bill me correctly, I can't be bothered to pay.

So yah, admin mistakes. Deliberate ones.

Insurance just pays, they don't check the coding as carefully (how could they, they were not at the appointment).

An extremely common "mistake" (up-coding) is increasing the length of the Dr. visit up a level or two. Take a watch with you, and check how long the Dr. was actually present with you, then check the coding. (And paperwork and nurse time is built in, so it's not necessary to account for that when checking.)

They'll also bill for services they talked about, but didn't actually do.

And they'll code separately for a service that's supposed to be bundled with another code.

I've seen every one of these.

Because as a well-compensated engineer with good insurance, who pays his bills when possible at point of "sale"/leaving the office, some how in the last 20 years I've had several occasions where mystery charges came in the form of paper bills that I had to make several calls to get to the bottom of, sometimes 3-4 different amounts on different bills.

The US health care system is crazy in many ways, but hospital/doctor office billing and admin is one of the more egregious. I firmly believe they make money by people simply paying every statement they get, some of which the insurance company will later take care of anyway, just out of fear of these "collections"