When I first started selling Rights back in the early days of the commercial internet, I intended only to sell 20 and let the potential owner of the Master Rights sell an unlimited amount.
However, as time and business progressed it didn't take long to realize that I would be disadvantaging the original Rights owners who had paid a substantial amount for international coverage, as the Master Rights offered. So the Master Rights offer was quickly withdrawn without any being sold.
The offer lives on in perpetuity of course for as long as I keep the original offer on my current manual, but it is not being offered at any stage now.
As for separate country Rights, that's fine in principle but hard to police unless you have total control over the resale. That probably means accepting and processing payment for your Rights holder, and guaranteeing them authenticity of accounts. That's harder to accomplish to the complete satisfaction of both sides.