When did AZ Hwy 666 become Hwy 191? It's still Hwy 666 in NM & CO.?

I traveled over that Hwy 666 in the 1980's and now find it's been renamed
Update: Alex, look on a map in the SW corner of CO and NE corner of NM.
Porsha-good answer-I was looking for dates about when that change occurred. Strange that CO & NM didn't make that change.
Update 2: Not surprising that it's not too far from four corners. My wife took a picture of me under the Hwy 666 sign and missed the whole 666 bit. It wasn't in the picture.
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