@greatnameguys Similar situation, but I think it happened through a different process. State Route N used to reach Platte City, but it was truncated at some point and now terminates at Route D. This is reflected in MoDOT data, and you can follow the signs on Bing StreetSide to confirm. OSM seems to have chosen "Old State Highway N" as the name of the northern stretch, which I think is fine. The tag old_ref="MO N" is also warranted imho

@Baloo I don't know much about WA, but MO supplemental routes ("lettered routes") don't always behave like normal state highways. To quote MO's MUTCD, "[u]sually, but not always, double letter routes are farm to market roads that end at county roads" (MoDOT EPG 943.1). It's pretty normal for the pavement on these routes to unceremoniously end and dump you into a tangle of county roads. There's usually a little M19-2 sign that says "MoDOT Maintenance Ends" right next to the pavement transition. Hence why I was focusing on pavement: it's not sufficient to prove a handoff of authority, but that's where it'd be if one exists.