I'm not sure on the exact timeframe, but New Mexico had a massive renumbering for its state highways around the early 90's, mostly for smaller roads. I have an older map that referenced it, but was published after the renumbering so didn't actually show the old highways. I recently bought a book about New Mexican mountains but it was published in the early 70's, and it's hard to follow the author's descriptions when the highway numbers are no longer consistent.
Has anyone ever seen a list of the old highway numbers and their corresponding new numbers? I couldn't find anything online.
I think Steve Riner's site (http://www.steve-riner.com/nmhighways/NMHome.htm) might answer the questions you have.