CoL, CoS - regardless of the specific book, we need to discuss this. The specific book will just be part of that discussion.
Short version: A legal instruction is any instruction, posted in the turn chat instruction thread at least one hour prior to the start of the turn chat, by a citizen empowered to do so, within the limitations of the office the citizen is representing.
If you note, there is nothing about the "Will of the People" there, no about polls. Very intentional.
An instruction is a statement to the DP that they are to do X. The DP is a busy person, being pulled in many ways. The DP should be responsible for making sure a given instruction is within the boundaries of the office that posted it, and that is all.
They should be able to assume that the instruction represents the will of the people. As such, if they follow an instruction that is later determined to be against the will of the people, the DP is not responsible, but the person that posted the instruction.
Let's declare that anything in the instruction thread is presumed to be a legal instruction (assuming an office has not overstepped their boundaries). If we have a problem with an instruction, we take it up with the person that posted it.
Of course, that raise the question of how does a leader determine the will of the people, but that's an easier discussion.