Knowing that this 1.0.3 update is coming, I have not moved beyond the SGS/Junktown/GMS starting area, because I heard that many zones will be updated. Someone mentioned that zones you haven't been to yet are the ones that are updated by the update.
Is this true? I haven't moved to Camp Hathor yet, because I want those (and all other) zones to be created by the maps from the new update. Is this the right idea? Should I hold off on venturing beyond the pre-Depot A areas until the update is officially released?
Or does this have no bearing on the maps, and I should just go to Camp Hathor now?
You mind as well just update to 1.0.3.20 now and be done with it. The Experimental Build, despite its name, is very stable in its current iteration, and--as Hazard mentioned--any serious bugs are swiftly patched by the devs upon them being reported.
There
are new zones that have been added in the Lower Caves between SGS, Junkyard, and Camp Hathor, so it's not
just the Lower Underrail metro area that has been updated for the map. However, these new zones are nothing more than empty connector maps meant to fill the space between existing rooms (at least as far as the Lower Caves are concerned), so don't worry about having a ton of content behind you that you'll have to re-visit in order to map out. I can tell you now with confidence that it's really nothing to worry about.
Regarding what zones are and are not updated, it is my understanding that
everything is retroactively updated once you download the update, regardless of whether you have already visited it or not.
tl;dr :: You mind as well just download 1.0.3.20 now from the Steam Experimental Build and be done with it. Your character will be fine. Don't worry about it. If you're not sure how to download the Experimental Build, there are instructions on the Steam forums somewhere. Or you can just ask for help here and I can explain it. It's a fairly easy process.