Following items not being shown as completed, despite being added to appearances tab.

• Ceremonious Pauldrons
• Ceremonious Greaves
• Ceremonious Helm
• Ceremonious Breastplate
• Ceremonious Gauntlets
• Ceremonious Waistguard
• Ceremonious Armguards
• Ceremonious Sabatons

Crafted weapons do show as completed appropriately.

if you SHIFT+CLICK anywhere in an ATT list, does the collected state get fixed? after you do it, you should get a chat printout saying your collection has been refreshed. (i don't have a SL blacksmith/plate wearer, so i can't test for this issue personally)

No, unfortunately refreshing the collection doesn't help. (I've noticed the auto-update is inconsistent at times so I refresh pretty often). I'd be curious if it's the same for other armor types, haven't gotten into SL with any of my alts yet.

I was able to reproduce the issue. We'll look into it more and come up with a solution soon.