Address is correct in Contacts, but Maps munges the address.

Yes, I agree, the problem with Maps corrupting valid addresses is a broad problem. My futher experimentation shows that this can happen to any addresses I specify in Contacts. It also happens when I type "give me directions to (correct address)" into Siri. It also happens if I Message someone the address: when they receive a message with the address and click on it, Maps will open, corrupt the address, and direct the recipient to the wrong place.

So it looks like Maps is struggling to "improve" Map addresses: If Maps receives a perfect address from another app, Maps will try to "improve" that address, potentially resulting in a very different and wrong location. This leads to mis-routing and other location-dependent failures. This happen within both the MacOS and iOS ecosystems.

If Maps has ever taken you to the wrong place given a correct address, it is probably this Maps address improvement service corrupting your correct input. It's not you, it's maps.

The other address is about a mile away in the same city.

It is important to note that my home address is "rewritten" sometime between Contacts and Maps (and elsewhere) . So I start off with my home address (for sake of argument, "300 Oak Avenue") in contacts, but maps rewrites it as "300 Oak Highway" and pins my home at that other address a mile away. If I type in "300 Oak Avenue" in maps, that's A-OK. If I'm literally at Home and ask for directions to Home, Maps will build direction to 300 Oak Highway, a mile away. Throughout all of this, my address in Contacts remains correct ("300 Oak Ave")

It seems to me that something in the Maps API is trying to "improve" my address as specified in Contacts, but instead gets it wrong and corrupts it. Oh, and both of these addresses in question have been on the books for 75+ years, and have always worked when directly entered into Apple maps and all other mapping software I've used.