If it's neither safe nor convenient to look up the non-emergency number, it's an emergency. Any armed stranger at your door will only wait so long before forcing escalation.
The alternative is: while you're ringing the non-emergency line, he sticks a gun in your face, "arrests" you, and helpfully hangs up the phone. You didn't transmit E911 data-- and nobody will come check on you.
If your iPhone is allowed to call 911 over bogus telemetry, it's good faith enough for two humans to use it to verify officer credentials.
The system I want is basically something simple citizens can use and can become common practice. Such as cop shows up and you scan their badge with your phone. Why? Because such procedure can kill police impersonation before it starts. It creates a high level of difficulty to perform that impersonation. Honestly, this should even be possible without an Internet connection. There is also an added benefit for both parties. The scanning of the badge logs an interaction and can make both parties accountable.
That's the alternative. The alternative isn't do nothing when I'm literally asking for something else. Get the context of the thread before replying. It's like you're pretending my original cert question doesn't exist.
I guess someone could run a Stingray and re-route your 911 call to a hostile party but at that point, I don't think a CA would help you given that they are right outside your front door.