Attila:
Incidentally, there was a rate of climb limit in the Flight Manual, not to exceed 2000 ft/min below 2000 ft agl
I don't know whether this is an example of it, but the avoid region is only applicable for unaccelerated level flight. If you're in autorotation or even a low-power rate of descent, the avoid region is very much smaller. In a high-power low-speed climb, the avoid region (if the manufacturer had to depict it), would be somewhat bigger than the one in the handbook. As Attila notes, the 214B was capable of very high rates of climb since it had a Chinook engine in what was basically a Huey.