With 11.0.7, Blizzard made an effort to fix the retroactive all quest reward transmog unlock.
In some cases, their fix worked. I unlocked the cloth armor reward for the Venthyr quest campaign that I completed on my plate character.
But in the case of the transmog from the BFA War Campaign, I have not unlocked the other armor type appearances that should have been rewarded.
An example: I completed the quest Mischief Managed on my Plate character. He received the plate transmog appearance reward.
I have not received the other armor type rewards such as 7th Legionnaire’s Monnion for my mail armor characters. I believe this to be a bug inconsistent with Blizzard’s stated goal of retroactively rewarding all possible armor type appearances from quest completion.