Correct, you’d have to re-run sub python3*Packages.inject. When you run that query, it gets resolved to the actual packages, and the subscription is added to those. There’s no notion of subscribing to globs, at the moment.
It’s never been built by nixpkgs-update though. You can see that because it’s missing from here.
EDIT: actually, no 3.13 packages have been built by nixpkgs-update at all. I’m not immersed in the Python subsystem so can’t tell you why, but I’m sure there’s a Good Reason™.