Navajo Jewelry: 1st, 2nd, and 3rd Phase Time Frames?

Okay, here is why I’m confused. The following photos are pages from two different, highly respected books.

This photo is from Indian Silver Jewelry of the Southwest 1868-1930 by Frank Holbrook c. 1978 and is calling the two closed-center concho belts “first phase, circa 1885”

This photo is from Southwest Silver Jewelry by Paula Baxter c. 2001 and is calling this closed-center concho belt “second phase, circa 1880s-1890s”