Not really overbooked, so much as you put down you had a sore throat which takes about 10-15 minutes but now you're here can you have your ear looked at and also your stomach hurts but it started about six years ago and you think you might have ADHD so could you get a referral for an evaluation?
I'd argue that if that's consistently happening, you're overbooked. If you book more people than you can reasonably expect to serve on time, that's being overbooked.
I see that as no different as the shitty companies that have an IBR that repeatedly tells you about 'higher than normal call volume' no matter when you call and anytime you call for months/years. At some point you know your normal and aren't staffing or booking at proper levels.
I work for a psych clinic where the head doctor rarely turns down same-day appointments, while his schedule is fully-booked to see multiple patients/15-20 mins. We've slowly bled providers over the course of the last 3 years and haven't really replaced any of them. Turns out, it's hard to hire when you have a reputation for low salaries and nefarious contract negotiations.
Each specialty may have their own story, but we definitely see constant issues of being overbooked AND understaffed.