It says I have not collected the items Dread Corsair Greathelm and Dread Corsair Pauldrons, which are quest drops from quests Storm's End and Storm's Judgment respectively. I have, however, completed the quests but those 2 items were not awarded.

In my Appearances tab the items show up when I filter for them, but they are not listed by the specific name:

Just to be sure I also got a separate addon to confirm that I had completed the quests:

Edit: The same problem occurs in Tiragarde Sound for the item Sea Raider's Spaulders, related quest is Fairwind's "Friends".

Azerite armor is special. As we found out in our discord.

Any quests that award Azerite armor will only give you the transmog for the one you got. The other two pieces you will not receive. Most of this armor is offered again later in another quest, but not always. This is something done by Blizzard and not something we can control. You can see this in the Alliance campaign (finishing up Horde) when the quest offers you a piece you only receive the one.

Unfortunately there isn't much we can do, but some pieces have "Shared" appearances that may or may not be faction locked. What we can do is take an individual look at each and see what we can figure out. At the moment I'm in class so it's something I'll have to look at tonight and see.

I know this isn't exactly the answer you or anyone wanted to hear, but sadly that's how Blizzard has it working currently. We keep hoping they change it so you gain all the appearances when finishing a quest like you do the others, but suspect it has something to do with how Azerite armor works.

Thanks very much for the reply! It's a great answer at least it put my mind to rest. I got a little spooked thinking I didn't finish the quest when I was quite sure I did.