MDG: Rabbi Lamm does not mean parts of Torah are untrue, God forbid.
What I believe R. Dr. Lamm meant is that everything in the Torah is true, but the Torah itself, as we know it, does not contain all the Truth that’s out there. Some of God’s Truth (i.e., the fabric out of which the world is fashioned and in accordance to which the world runs, and based on which people should act) is revealed to us in the Torah – sometimes explicitly other times implicitly. But that is not ALL the Truth. Some Truths are not revealed in the Torah, but instead were left to mankind to discover over time. These Truths are the “maadah” half of Torah U’maadah, and the “derech eretz” part of Torah im Derech Eretz. These Truths are uncovered by biologists, politicians, historians, psychologists, doctors, lawyers, philosophers, engineers, mathematicians, chemists, generals, ect.
By combining our knowledge of Torah Truths and Derech Eretz (or maadah) Truths (always using the Torah’s guidelines to determine what aspects of the non-Torah world are indeed True), we come to a fuller and more complete understanding of the Whole Truth.