I completed the shadowmourne quest line on 12 plate wearers a while (possibly years) ago. I learned the mount and toys and kept the tabard and neck on my main DK, and put the other 11 of each item in a guild bank (The Green Shield - Galakrond)
I noticed today that the following items are missing:
4 Tabard of the Lightbringer
3 Muradin’s Favor
2 Sylvanas’ Music Box
3 Reins of the Crimson Deathcharger
2 Jaina’s Locket
I believe this may be caused by deleting some of the characters who earned the items, even though the items were not housed in their personal storage, but rather in a guild bank.
the deleted characters were:
Artichoke - Drenden
Foghat - Galakrond
Cowhide - Kal’Thuzad
I do know for a fact that I had 11 of each one in the guild bank, as I had used the warbank to consolidate them all on one server, and then a few days later, I got a wild hair to clean up my roster.
Edit: my wife and I are the only members of this guild, so the items were not withdrawn by someone else.