In essence, this gear works like the gear tokens from the Timeless Isle and as such will drop for specific armor types.
“The new BoA Black Empire Catch-Up gear is very similar to the Timeless Isle BoA gear. It drops from random mobs in the Uldum and Vale of Eternal Blossoms invasions and has the appearance of the LFR Ny'alotha sets.”
For each armor type, there are two possible pieces of Azerite Armor per gear token. Additionally, four potential pieces of gear per token exist for the other gear slots.