Well it sure does look like an old alignment of MO 21 that got chopped up by the modern one. Let's consult yet another government database!

https://data-msdis.opendata.arcgis.com/datasets/MSDIS::mo-modot-roads-routes/explore?location=37.649428%2C-90.670558%2C17.59

^ That's the best online resource for Missouri-owned roadways in my experience. It's the same data that's used in MoDOT's HPMAP.

It says Bluebell is a privately-owned road, but Morgan is an East Outer Road 21. Indeed, Iron County calls them Bluebell Lane and Morgan Lane. It's neat that some of those parcels still call it 21.