I remember raising this on the AARoads forum, as I was preparing to activate usanm. The reaction from people from the region was about how much of a joke is route signage in New Mexico. That's consistent with my own experiences in other parts of New Mexico. That is probably the state where route signage is most worthless.
My research in 2011 State Transportation Commission minutes found some confusion about where NM 528 went west of former NM 47, but its segment east of former NM 47 clearly was officially removed from the state highway system.