Openmw additem is different from vanilla additem
Bug or Feature? not sure.
Notice the negative value.
I tried, additem "anyitem" -1 , to an npc in openmw, it does not work.
I tried in vanilla, it works but a bit buggy.
So basically a negative values means the added item will restock. This is useful and highly recommended because, that way you can add a restocking supply to a merchant using scripts/console.
In vanilla, the negative values worked but it a bit messed up from my test. Using additem with negative values on merchant npcs will give the items to them, but upon checking their inventory, the item count is around 64k to 65k. Thats a huge number! (dont know how this happen)
The additem with negative value is also mentioned here http://en.uesp.net/wiki/Tes3Mod:AddItem#Count
(RM-4118 from redmine: created on 2017-09-19 by Randy Davin, , closed on 2018-01-02 by nobody)