> The things located at the URL may have names or identifiers, but by design of the web the stuff located at an address is mutable while the address is immutable.
> I'm not sure about that. An address makes no promises (technically speaking) about what you will find at that address.
I don't see how that's relevant. An address, in principle, merely designates a particular location, perhaps physical like a street address, or logical like a memory address. In the context of a search or lookup, you can obtain what's contained at that address.
Similarly, a URL designates a particular resource location, as exemplified by its full name, Uniform Resource Locator. In the context of a client/server request, you can similarly obtain a representation of what's at a URL.
But an address is a designator/identifier.