But he did make reference to them right after Sraffa brought them up, directly replying to Sraffa.
Yet made reference to “natural rates” but Hayek never refuted Sraffa’s criticisms.
Read your fellow Austrian Robert Murphy:
“In his brief remarks, Hayek certainly did not fully reconcile his analysis of the trade cycle with the possibility of multiple own-rates of interest. Moreover, Hayek never did so later in his career. His Pure Theory of Capital (1975 [1941]) explicitly avoided monetary complications, and he never returned to the matter. Unfortunately, Hayek’s successors have made no progress on this issue, and in fact, have muddled the discussion. As I will show in the case of Ludwig Lachmann—the most prolific Austrian writer on the Sraffa-Hayek dispute over own-rates of interest—modern Austrians not only have failed to resolve the problem raised by Sraffa, but in fact no longer even recognize it.
…
“In summary, Austrians should familiarize themselves with the construct of a dynamic equilibrium, in which spot prices and other data can evolve over time, but where entrepreneurs fully anticipate such changes and squeeze out all pure profit opportunities. In this setting, there is no such thing as an objective real or natural rate of interest, so the Austrians cannot cling to their prescription that the banks ought to set the market rate to “the” natural rate. However, as our last scenario above hoped to convey, it still is true that an intertemporal, dynamic equilibrium can be disturbed if commercial banks inject new money into the credit markets. If a Misesian boom-bust cycle ensues, the reason is not that the banks charged a money right below “the” natural rate, because there is no such thing."
Murphy, “Multiple Interest Rates and Austrian Business Cycle Theory,” pp. 11
http://socialdemocracy21stcentury.blogspot.com/2011/07/robert-p-murphy-on-sraffa-hayek-debate.html