Thanks! I was pulling from the 2019 TIGER Places shapefiles for New Mexico. I'd imagine the entire state could likely use updating, instead of just the single city of Los Alamos.
https://www.census.gov/cgi-bin/geo/shapefiles/index.php?year=2019&layergroup=Places

Go ahead and revert back to the original 2008 TIGER administrative boundary if you're able. I thought I was doing things correctly with a new import using JOSM, but maybe I should have updated the object instead of trying to replace with a new shapefile?

Looking for guidance as to why this upload of the current, revised administrative boundary is not showing in OSM. Do I need to delete the old boundary first?