Well, the lords should be the only ones interpreting the laws, magistrates should only execute a lord's edict and bring anything which isn't cut and dry to her attention. The whole point is underscoring the fact that justice, peace, and harmony all spring from the lord and her stewardship.
Of course, this is all theoretical, and, I daresay, rhetorical in a land such as Wayside where power is not descended from lords but, instead, comes from a plutocratic oligarchy. Here, the rules are different for, if I understand it correctly, the Magistrates themselves are a kind of guild, or an extension of one at the very least. As such, it's very likely a magistrate can and does hold supreme mandate over the law and can exact its edge at her will. One would need seek an Arborian law scholar for a more precise understanding.
Master Dramthin Hartsboon
Simple Keeper of the Tainted Grove