Hi Ethan,
For some of these documentation catalogs, that is indeed the case today - and the one generated with the Diagnostics that are hosted on docs.swift.org are included in that set. Today, that content is updated roughly nightly, using the content that's in the current main branch of the swift repository.
It's actually two workgroups that have been aware of this - both the documentation workgroup and the website workgroup, who have been working out how to address this (unfortunately longstanding) issue with all the content that's hosted and linked with swift.org.
We have some techniques that we believe will be able to sort out hosting versioned documentation, but the whole system to 1) map the content to versions and release it as such and 2) host that content in the infrastructure that supports Swift.org is all work-in-progress. It's been a topic in both workgroups, and the Information Architecture workgroup over the past several months, so if you're curious about the details, I'd be happy to help point you to them, or provide more specifics.
The gist of what we're aiming to do is build multiple sets of docs from both main and the current release branch, do the work to support selecting between two sets of versioned content (as that's not directly supported in the DocC infrastructure today) and tie that same process into the website redesign efforts, so that the documentation more seamlessly connects into the swift.org website content, both grow the space to contribute to documentation and consolidate where it lives with the recent docs proposal, and update the back-end processes to support generating this content and linking it into our release processes to support initially two versions of the content, growing to more as we iterate through releases going forward in order to establish a history of supported, versioned content.
In short, we definitely recognize it's a problem, it's a problem across our documentation that is linked from swift.org, it's been there for years, and multiple workgroups are engaged - actively working to solve it.