Once ago, I had a warlock circling Nagrand for Khorium nodes. When I found one, Id loot it.

Then I got an idea to not auto loot it, and leave the motes of earth in there... only looting the Khorium ore, and leaving the node intact. 5 mins later, Id circle and see it still there, Attempting a loot... finding only motes of earth...

I logged another character, another account, went to the node, attempting a loot... finding only motes of earth.

Moral of the story is.. once a node is tapped... its done.