What you are saying is true; what I was keeping myself confined to are the codes that you have reasonable assurance that the client will actually do something with. A lot of those codes will not cause the client to do anything terribly specific, like "follow a redirect"; it'll just return the content as if it was a 200, and if it's an API, maybe return the request as failed, but that's about it. In the vast majority of cases, clients don't particularly care if they get 400, 401, 403, 404, or indeed, 4xx.

I wonder if there's even a single client in the world that will get a standards-compliant 412 Precondition Failed and try a second request with a different set of conditions. Or indeed do anything sensibly different at all vs. having received a 404. (I specify "standards-compliant" because I'm sure there's plenty of APIs that use 412 for something non-standard.)