I dug a little and found that Stone County does have a coherent road identifier system near Table Rock Lake, but I guess nobody's pedantic enough around there to care about it 😊

Since we're right next to Table Rock Lake, the U.S. Army Corps has some public domain maps of the area. This one from 2016 shows State Route DD leading into a county road named DD-25: <https://commons.wikimedia.org/wiki/File:Table_Rock_Lake%2C_Missouri_and_Arkansas_-_USACE-p16021coll10-10699.pdf>

This old map from 1986 (not copyrighted in US) agrees with the USACE map: State Route DD ends at some point with "LR DD-25" picking up the slack: <https://digital.shsmo.org/digital/collection/Maps/id/1132/>

This old photo from 2003 looking southbound along DD corroborates these maps: <https://datazoneapps.modot.mo.gov/aran-external/Home/AranImage?y=2003&t=2939&i=28874990>. Continuing, the name is "Table Rock Lake Road DD-25", and the road branching off to the left is "Table Rock Lake Road DD-24". Check out the name_1 tag on Lake Bluff Drive..."Dd-24". You can also make out the little 'maintenance ends' sign in the distance

Putting it all together, I now think an appropriate tagging setup would be to split DD at this point, replace ref="MO DD" to the south with ref="LR DD-25", add a route relation with ref="DD" and network="US:MO:Supplemental" from this point north to MO 13, and add name="State Highway DD" (or loc_name?) from this point to Coney Island to address the local familiarity issue while not affecting semantics of supplemental route tagging (@Baloo We've both nuked a lot of redundant name="State Highway XX" tags, but this would be an exception)

Thoughts?