Something to Think About over Leining

The Mekhilta on our parsha records a Tannaitic dispute whether Yitro's visit to the Jewish people transpired before or after the giving of the Torah. Many centuries later, the Ramban discussed the argument, explaining each side's rationale. In defending the view that the Yitro narrative occurs after Matan Torah, he writes:

And [this opinion] is certainly aided by the verse which says . . . "And I [Moshe] inform [the Jews] of God's laws and his Torah," (18:16) . . . for they were given at Har Sinai!

Moshe describes to Yitro how he sits as judge of the Jewish people, adjudicating their disputes with Torah law. If this conversation took place before Matan Torah, then to which "laws and Torah" does Moshe refer!

Surprisingly, the Ramban ultimately concludes against this apparent disproof and claims that the narrative did indeed occur BEFORE the giving of the Torah. The Ramban leaves us to answer his own troubling question: which "laws and Torah" did Moshe use?!

Were they identical to those found in our Torah? If so, what level of authority did they carry? What is the value of a Torah pre-Divine Command? If not, how does an alternate set of laws change our understanding of the Torah's role? By what right did Moshe (and perhaps Hazal in his footsteps) legislate with a set of non-Biblical statutes?