It is obtainable from the current raid tier. If you want mythic tier gear, you need a mythic base from the raid.
Again, how did blizzard use these terms?
Tier set = set designed for that tier
Set bonus = set bonus.
I never said anything about off pieces, YOU did. You want to call them off pieces because you dont want to separate tier gear from set bonuses.
There is 0 reason anyone should be confused by this system. It just shows how dumb the playerbase is. You could have either read the blue post, and if you didnt, you hover over what your item is going to convert to, a basic to any mmo ever so you know exactly what you are getting.
If you do none of these then you are deserving of what you get. I swapped a chest piece… do you know why? Not only did I read what the hell the blue post said, I know that the set bonuses were only ever created this tier on the 5 main item slots. I knew Blizzard was referring to the tier set as the whole. Whenever they show you a new tier set, its not just helm, gloves, shoulders, chest and legs is it? No, it shows everything and they label it as such. They did this prior to transmog ever existing.
Learn to convey what you are trying to say without giving a word 75 different meanings which confuses people for some reason even they it was spelled out in blue letters.