Each era has its own strategies, and there is no perfect system right from the start. Truly effective rules are always formed through the "friction" between different interests.
The Nirvana Plan was crafted in haste, so even though it was well designed, it could not possibly account for all situations.
Since its promulgation, the system has undergone countless changes; some were decisions made at the local level, others were central orders.
However, if there were no "accidents" or "protests", many people would have just barely got by... Obviously, some things cannot be compromised.
At least, the original designers might not have considered the scenario where, once the exploration of the Foreign Domain encountered a "major failure", there would be the question of whether or not to impose heavy taxes on the spoils of war for the survivors….. Strict implementation of the system would be possible, but then, it would hurt the people's morale.