At least as this article describes it, it's not even predictive on its face. He did not assess "fresh" couples, and come back a few years later to see how they

At least as this article describes it, it's not even predictive on its face. He did not assess "fresh" couples, and come back a few years later to see how they fared. Rather, he interviewed people who were already either having trouble or they weren't. Although I haven't studied it for proof, I have to assume that the interactions of a honeymoon couple will be different from a couple in trouble, even if the honeymoon couple is destined to have problems. Thus, he's not able to interview the honeymoon couple and determine what their prospects are.