Very pedantic of me, but I figure it’s interesting to note: technically a release on PyPI can have zero files or even one or more wheels but no sdist. The former is a degenerate case that users don’t normally see, and the latter happens if the user chooses to only upload wheels (or their sdist upload fails for whatever reason).
reply(This doesn’t change your observations at all! Just as a demonstration of how Python packaging’s data model can be unintuitive.)
I'd argue that the latter's a degenerate case as well--for the somewhat nitpicky/minor reason that package managers' errors are extremely poor at indicating the difference between "the version you asked for doesn't exist" and "there are no artifacts compatible with your platform at the version you asked for (and, for bonus points, here are some artifacts that are compatible with your platform)".
replySomething that I wish was included in PEP-694 is the notion of a "tombstone" invalid/empty sdist artifact to deal with that case, to make it easier for package managers to interpret and surface those different failure classes.
Like, sure, this is a package manager UX problem, but it's been happening for long enough that I feel like it might be time for PyPI to help managers do better.