Does this mean that only the current release receives updates (including security updates) and fixes while older/all other versions do not?
Quoting from the openwrt website https://downloads.openwrt.org/
" Historic Releases
The releases linked here are mostly for historic interest - they are long out of date and completely unmaintained. "
But on the Table Of Hardware, many older versions are recommended.
A related question is asked here (OpenWRT and Current Release Support) but it does not address this.