I ordered a full suit of iron armour for each of my planned fifty military dwarves. I used the manager to assign the jobs, as I usually do, so that I'd get the exact number of items made. The first three squads had their armour and were training happily. Just a moment ago, some migrants arrived, so I quickly assigned twenty of them to fill up the remaining two squads. I noticed they stopped gathering equipment pretty quickly, and when checking the stocks menu, discovered that there are significantly less iron armour items than I'm sure I ordered to be made (28/50 shirts, 26/50 greaves, 54/100 gauntlets etc). I'm 100% certain that I ordered the right amount, as I sat working out how much hematite I would need to mine to get exactly the number of items. To add to the mystery, some of the remaining items as well as those worn by the first few squads, are apparently 'showing some wear'. They've never been in real combat yet!
I have no idea why this is happening. My fortress' only entrance is a bridge over a volcano. There are some tunnels filled with magma running underneath the stockpiles (for the forges and such), but iron is magma safe. Besides, I don't think a few tiles of magma one level below would melt nearly half of my armour collection. I don't think it's kobolds stealing it. My three tile wide entrance has a dog penned in the middle of it, there are always dwarves running about the stockpiles and the entrance, and I doubt kobolds would steal several hundred pieces of armour in just a year.
What the hell is going on? Here's a full list of things that have gone missing:
22 mail shirts
24 greaves
21 helms
46 gauntlets
40 high boots
No shields (perhaps because they are made of copper as opposed to iron?)
No shortswords (these are iron, however)