I have created a web-site that shows all of my cloud renderings of the samples. It is available at victorz.ca/misc/3d/.
At first, 1 render = 1 cloud unit, when the service was called Autodesk Cloud with its subordinate *Autodesk Cloud Rendering*.
Later, they renamed it to Autodesk 360 and its complement *Autodesk 360 Rendering*, and made 1 render = 5 cloud units. They also upped the limit to 75 cloud units, and made me have 50 used up (10/15 renders), which is nowhere near the 160 renders.
Still, I noticed a flaw: the cloud units are not subtracted until after the rendering is complete, which causes the following effect, -10 cloud units (-2 renders) remain when I sent 3 renders on the last credit.
To reproduce this, just send multiple renders when you're on your last credit.