Formally speaking, standardizing “Old Highway 123” names is not a goal at all for OSM. You can add old_ref=* to individual ways when a decommissioned route leaves behind roads clearly named after the route, but name:etymology:wikidata=* is more useful for that purpose. In practice, old_ref=* has turned into a bit of a junk drawer of old route information. But your network=US:US:Old old_ref=US 123 ref=123 tagging even confuses this junk drawer with real-world historic route designations that are signposted on the ground.
I first noticed your historical route mapping a few weeks ago after you mapped Old Highway 58 in Barstow, California, as both a network=US:CA:Old ref=58 route relation and ref=CA 58 Old on individual ways. This is causing maps to variously show the number “58” (CoMaps, OSM Americana), an actual State Route 58 shield (Mapbox), or a “CA 58 Old” badge (OSM Carto).
I thought maybe you were thinking of this single guide sign along northbound Interstate 15 that pairs Old Highway 58 with a standard state route shield. But this sign is erroneous: the exit is at a location that would’ve been renumbered from 179 to 186 back in 1969 had Caltrans used exit numbers back then, and Old Highway 58 should not have a shield.
I wondered if maybe Caltrans had made enough mistakes along these lines that we could consider Old Highway 58 to have a shield unofficially. It would be pretty cool if OSM were the only one to notice. So a couple weeks ago, I took a big detour to Barstow to look for more shields. Unfortunately I could only find that one sign, nothing else. The guide sign is correct on the northbound lanes of I-15:
I don’t mind being led on a wild goose chase once in a while. I find surveying fun. But this is actively misleading people who use OSM more seriously to get around. We should not have a route relation for the former State Route 58 alignment – especially not one that continues where the pavement ends:
At the very least, you should’ve stuck to the old_ref=* tags on ways and nothing else. But since you’ve gone too far and brought all this historical mapping to the fore, we’re forced to probably eliminate even those invisible tags too.