Those two phrases do not lexically parse in identical ways, but we should not interpret the RFC to be saying the alternative of "I really tried, but boy filesystems are hard and maybe the NFS mount disappeared, and well shucks, couldn't find it! 404!".
We should interpret the RFC as written which is that this particular server could not find the resource. That does not mean the resource is not findable by this server at a different path or by a different server at a different host.
There is no defined equivalency between host1/one/path and host2/other/path, even if the resources returned could potentially be the same.
There is no retry formula for a 404 at one URL that might return 200 at another URL.
There is no defined meaning for the same resource at another location. HTTP 404 makes no attempt to comment on the uniqueness or commonness of a resource. No comment on whether that resource existed in the past, is expected to exist later, or in whose imagination it could conceivably exist in the future.
The HTTP response simply states whether the resource was found to exist at the specified location at the time of request. Any further conclusions drawn from a 404 are speculative.
Impressive given that it explicitly contradicts your point:
>the server can authoritatively state that the resource is not findable
>origin server did not find a current representation
Those two are not the same thing.