I may not be as specific in this post in citing Michael Fishbane's Biblical Interpretation in Ancient Israel (New York: Oxford, 1988), since the Sabbath is almost here, and I want to get this post done soon. But here's a point to consider: Fishbane assumes that biblical interpretation in ancient Israel was a response to a living religious community (168). He says that Israel had an operative law code, which needed clarification and explanation because people trying to obey the law naturally had questions (91). But could the interpretations have been part of a scribal academic exercise, meaning that Israel did not have a normative law code? Fishbane acknowledges that ancient Near Eastern law codes were not necessarily real laws for real life, but he thinks that the biblical codes were such because the Bible presents them as being taught and done (95).
Maybe at some point there was an attempt to institutionalize a law code for Israel. Ezra and Nehemiah present such a scenario. But the Bible presents the pre-exilic period as a time when the law was often not observed. Maybe the scribes were interpreting a law that they thought should be normative for all Israel, but which was not followed by many Israelites. As I noted in a previous post, there were different laws in ancient Israel: the priestly and the Deuteronomistic ones, for instance. Maybe both parties felt that their laws should be followed by all Israelites, and they rebuked the people for not doing so.
In the Second Temple period, there were different law codes as well, in a manner of speaking. Jubilees and the Qumran community advocated a solar calendar rather than the lunar-solar one of the Torah. In the rabbinic period, there were different halachot about the oral and written Torahs (or Toroth). Perhaps such diversity existed in the time of the "biblical period."