[cptskippy]

> In Targets case, it should have probably returned 400 Bad Client, since what the client tried to access wasn’t a REST endpoint.

The trouble with that approach is it puts the onus on the Server to response accordingly. In the case of a Client misconfiguration you might point the Client at a valid HTTP Server, just not the one you anticipated.

I agree with nerdponx that they were miss using 404. Instead they should have used a different HTTP Response Status Code to indicate something was removed from the system. Perhaps 410 Gone or 417 Expectation Failed.

[layer8]

417 is specifically for use with the Expect header, so would be a misuse as well. 410 would be fine, but is technically a sub-case of 404, so if 410 is fine 404 should arguably be too.