Sophia Sage — thank you so much for your response! And others too, I haven't read through all the replies yet.
One of the areas of confusion (here and elsewhere) is that people talk about different areas and kinds of numbness and other kinds of nerve damage as though they are the same, and they really are not, IMO.
I had contouring on my chin and jaw via incisions inside my mouth. The healing is a little weird, but there's essentially no numbness whatsoever. What numbness there is (a small area from my chin about an inch up toward my lower lip) results from the swelling, and it's not an issue. It gets better day by day, and there is feeling, just not quite 100% normal just yet. Obviously any surgery can lead to more serious nerve damage which can cause numbness, but that's I believe an unintended and somewhat abnormal complication for most procedures that don't involve a hairline incision, and the recovery from it is probably different, since we're talking about probably much smaller regions and probably not fully severed major nerves.
I also has a scalp advance in conjunction with "type-3" brow/forehead reconstruction. (That term was never used in any consultation, but you hear it around. Basically, I have titanium screws and plates in my forehead, which are completely unnoticeable.) People are talking about numbness in the forehead associated with that kind of surgery, of which I experienced none whatsoever. Zero. I could feel my forehead coming out of surgery, and the only thing that felt different was that there were some pulled muscles. (Like, literally pulled by the surgeons.) I don't understand how this procedure should, under normal circumstances, result in any numbness in that region, based on how the nerves work.
The issue I'm talking about is behind the hairline incision, about two inches on either side and stretching back four or five inches. It's obvious what the issue is when you see a diagram of the cranial sensory nerves:

Basically the nerves are cut along the hairline, and everything in green behind that doesn't work. From
Dr. Ousterhout's book:
QuoteTemporary numbness occurs with scalp advancement surgery because two sensory nerves, the supraorbital nerves, are unavoidably cut during the procedure. Patients will almost always experience a short-term loss of sensation in a fist-size area atop the head. Although 1 to 2 percent of these individuals may never regain their full sensation (similar to accidents and major surgery), the majority—the remaining 98 percent—will recoup normal to near normal feeling in six to nine months.
Obviously if you got an incision farther back (like what I hear regarding Facial Team) or endoscopically (Zukowski), you will not have this issue, even if perhaps you experience other complications. I had my own reasons for not choosing those approaches, but if the numbness is a major concern, they're maybe an option to consider more seriously.
Nerve regeneration absolutely happens — like, doctors reattach severed fingers and toes and worse, and nerves slowly grow back. The figure I heard is that they grow back at 1mm per year, but I don't really understand how that works -- like, do they grow out from the spine, or do neurons on both sides of the suture join together, or what? I'm not a neuroscientist or neurosurgeon, so I can't really answer. I have experienced numbness (in my big toes due to a lot of hiking in stiff hiking boots) that eventually resolved, so I know it can happen for me. But that was partial and a smaller area, so I don't know how it goes for a larger area like I'm experiencing now.
I do think it's unfortunate that this all isn't more clearly discussed, which is why I brought it up. There was a thread I found in the yahoo group archives (I think just titled "numbness") that had more personal stories, but it doesn't seem like it gets the attention it deserves. I am encouraged to hear people talking about how and when it comes back, and not just taking the word of the doctors who say it "usually" does, and the part I'm really missing is what it feels like as it starts to come back, what the recovery curve looks like, etc.
So thanks again for the responses!