A subdomain like 2002.gu.com would work without introducing changes to URL specifications, with the domain registrar giving control of that subdomain to the own

A subdomain like 2002.gu.com would work without introducing changes to URL specifications, with the domain registrar giving control of that subdomain to the owner of that year. But its such a niche case and also domains are probably sold because the old service is being shut down, so it would not work in most cases. I think an external service like archive.org that also captures redirects, so it can list all shortened URLs for a page, would be the better solution.