Yes, Status 3xx are not errors, they are (all?) redirections. 304 is a “redirection” to the asset your browser has already cached.
The devel versions are properly versioned (to the git commit) if you build it as a dependency, or with xcaddy.
Due to a bug in Go, these basic steps do not embed version information. If you want the version (
caddy version), you need to compile Caddy as a dependency rather than as the main module. Instructions for this are in Caddy’s main.go file. Or, you can use xcaddy which automates this.