They do seem to come in pre-set groups. We've had one group during 2 consecutive weeks, and so far no mirrors have appeared in 'another group' yet. Granted, we've only been able to record them for 4 weeks, so it is hard to say with certainty what their intended behavior is.
It's a shame that the mail armor set is almost identical to the base set. I really wish the colors were as different as they are in the other sets.
This needs to be updated for the people who don't use addons. Like where is "Inside House". Not told with /way or with numbers. Just with letters stating the location. It's frustrating to find them
You can add it to handynotes
This is a headache! Mine is not from the same group all week. Yesterday was group 4 & today is group 2! WoWhead news had group 3 yesterday. Maybe flying will make this easier but right now its a pain to have to go check all the Mirror spots to find the Broken one!