That's correct.
There's another software that will build an image with certain versions, patches, etc. I have not specifically used that to build a whole image (only to cross compile code to make a program for an OpenWrt device).
Maybe others can elaborate - or maybe even opine if that would be something easy to add on a firmware selector web GUI.
I mentioned the ease of use of the selector in another thread (in contract to one installing it themselves). It was after reception of mixed responses - mainly that I install it myself and assumptions I was ignorant for asking or mentioning issues with the selector.
Edit: also, you can select to install SNAPSHOT with luci-ssl - that should provide all up-to-date packages (but it all will be ahead of the current release - your terminology regarding that is somewhat a misnomer because yes, updated packages are no longer the released version 19, 21, 22, etc.).