"Cupboards and Wardrobes and End Tables are always safe containers no matter where they are."
Really ? Didn't know that.
I only recently learned this, too. Since then, my own experience has confirmed this. I've been clearing out everything from every dresser I've come across and putting a flower in its place.
"Some container types are set to be non-respawning — containers of that type will never respawn, no matter where the container is found."
http://www.uesp.net/wiki/Skyrim:Containers#Safe_Containers
That may hold true for the AM quarters but the room in question is 30. And I cannot support ANY cupboard and wardrobe being safe. Not from my experience.
My experience and the UESP article supports the theory that the cupboards and wardrobes are always safe.
My experience and the UESP article supports the theory that Hall of Attainment respawn time is 10 days. I've been collecting ice wraith teeth and few other ingredients from there for quite a while.