Good brief.
One thought for us to keep in mind as we watch this play out - there are ways these defendants can win and still not provide great comfort or clear resolution to the majority of situations (which of course is not their job).
For example, if the court were to agree (and be upheld on appeal) with the UIA analysis but limit adjacent corner access to the exact marked corners, finding that the defendant's GPS was insufficiently accurate but the evidence of specific corner markers in their case was sufficient -- defendants prevail. And then the court could reject (or remain silent) on the other rationales. This scenario doesn't fix the problem for all the unmarked corners.
Versus the court ruling (and it being upheld) that UIA adjacent access would allow for good faith understanding of corner location absent markers with GPS meeting this standard. That would be a slamdunk outcome for pubic land hunters.
Defendants win either way - but some ways are better than others for public land access.
One angle I wish they would have proactively addressed was how, "Provided, This section shall not be held to affect the right or title of persons, who have gone upon, improved, or occupied said lands under the land laws of the United States, claiming title thereto, in good faith" should be considered vs an arugment that "airspace tresspass" over their corner has an effect on a landowner's right/title to the land. You know the county will argue it, so best to get your view set preemptively in my view.