Adjusting Render Region boundary It seems that at times I'm able to see editable boundaries of the render region to make a small adjust to min/max X/Y and see corner grabs to adjust an X-Y boundary.   At other times I cannot get these and have to redraw the Render Region.   How do I get these adjusts to appear/disappear?
To get the adjustable boundaries, you need to make your camera active.
Simply click on it in the Outliner.