Well, as things currently stand, I'm going back to Smith Water's slopes this weekend. I notice that once again ( !!! ) my arrival will coincide with inclement weather, so I expect to once again be freezing and trying to spot objects amidst a light snow covering.
Oh well, it was fun last time, it will be fun this time
I'm not going to do anything radical - just going to fill in more of the increasingly sparse gaps in search coverage in the cell area. I would have gone to check out the chute east of the odor location, but OtherHand weaved down it so I don't have to! My mileage may not be impressive since it will be fairly slow going, walking around rock outcroppings and peeking into nooks and crannies. This time the firm plan is to head there across the flats and spend more time up there. Tonight I'll probably put together my planned path, and I should be able to make a screen cap and post it here.
As far as Bill goes ... he doesn't even have to suffer a leg injury or a head injury. Simple dehydration can also take a toll on both mobility and mental clarity, especially in a 65-year old person. We don't know for sure how much water he had with him, but it likely was not enough for the route he took.
There is something that bothers me about the terrain between Quail Mountain and Smith Water: it is kind of ... undulating. Even with strong legs and two hiking poles, dipping in and out of washes is a tough ask. Once you've slid down into a wash, you've got to have a motivation to clamber back out on the other side.
Of course, you could also follow the ridges ...
If he planned to get water at Smith Water, and let's say he had a compass and didn't take magnetic declination into consideration, he would have trended towards Smith Water in a somewhat easterly direction. Doesn't that fit in beautifully with OtherHand's theory? It can explain why he may have ended up in the cell coverage area, without pinging a tower if his cell was on, instead of hitting Smith Water further west, more in line with the Quail Mountain peak. And once you're up above Smith Water, the drop down looks really uninviting. He may have chosen to await rescue rather than risk life and limb on the slopes until a day or two had passed, and he was weakened from dehydration.
It is because everything seems to fit so well that I'm headed back to braid through existing search tracks one more time. I think this will be my last visit to this particular area.
I have another theory of sorts, based on the fact that, despite living in a desert region myself and being quite used to heat by mid-summer, I get very lazy for steep climbs when it is hot out: That Bill may have decided to approach Smith Water via Covington Flats instead. There is a low ( relative to the rest of the geography ) hill northwest of an unnamed spring in that area. Search teams have searched the spring and the wash it is in, but no-one's been up on that hill. I'm also aiming for that hill this weekend, separate from the Smith Water trip. The said-to-be less accurate of OtherHand's coverage maps suggest a faint lick of coverage on that hill. That's good enough for me

So, along with the better established search area, this is my long shot. I think it is much more likely that Bill would have pinged Palm Springs from that location, but I'll examine the northeast face of the hill, where Bill may have been shielded from Palm Springs towers. My theory is that he decided with the water he had and the temperature and time of his arrival that Quail Mountain didn't sound good, and he headed west on Juniper Flats road and up into Covington Flats, maybe with an eye on this spring or on the mining prospect nearby. The spring looks dry on Google satellite view ( and Smith Water's slopes look reasonable on Google satellite view! ) so he may have found himself out of water and out of luck. Why would he be up on the hill? I'll assume he knew Palm Springs can be visible from this area, since he drove down Keys View road for a look before stopping at Juniper Flats, explaining both his later than expected arrival at the trailhead and his knowledge that Palm Springs can be seen from the right elevation inside Joshua Tree, and thought that heading up the hill would allow him to place a call. Why didn't he go to the southwest side of the hill for a better line of sight? Well, I don't know.

If Bill did things that looks logical to us armchair theorists, we would have found him by now! It is easy to spin a theory and assumptions. When you take them to the field, they crumble just as easily!