Thanks for sharing this write-up Max. I had researched a bit of this strange history in making some edits to the Nevada US 95-related articles on Wikipedia years ago, but cool to read about it with some additional AASHTO documentation that I didn't have access to at the time.
It's a really weird configuration, and I think it may have been weird even 30 years ago when Fernley was a postage stamp on the map.
I imagine NDOT isn't going to clarify the situation there until they decide on an I-11 alignment (and I imagine that the USA Parkway to Silver Springs to Schurz "line" will be the favorite. But it seems like a better mainline intersection to the US50A expressway would make sense. Also would make sense if the I-80 guide sign to Las Vegas was for 50A and not 95A.
Yeah, the whole US route configuration around Fernley doesn't make sense from the typical route assignment perspective. US 95 Alt (from Schurz to Fernley) as it exists today makes sense with historical context, but less so once US 95 mainline was diverted out of Fernley. US 50 Alt makes no sense either. As neither alt route is comparable to their mainlines, they wouldn't get numbered as alternate routes today. But I imagine that this was NDOT's way of keeping all these highways on the US highway system given the options available at the time all this happened (as I'd guess they were less likely to get a 3dUS number and "spur" didn't seem to be a banner type).
The I-80 guide signage is a little bit wacky in both directions and inconsistent for all three Fernley & Wadsworth interchanges, given the configuration. For eastbound, an identical US 95 Alt South sign for Yerington & Las Vegas is actually placed before the West Fernley interchange (westbound as shown in the blog it's placed before the East Fernley interchange). But signing US 95 Alt South for Las Vegas isn't unreasonable—the US 95A/Yerington and US 50A-US 50-US-95/Fallon routes are similar distances with US 95A being about 3 miles longer (but shorter if you know some of the back roads to bypass Yerington). But I have always thought it odd that Las Vegas isn't signed with US 50A as well since, historically, more Vegas-bound traffic tends to go that way—I'd guess since they already had Fallon and Ely on the signs, they didn't want a third city based on MUTCD.