June 10, 2018:
From 1966-76 ish, Althusser self-critically re-examined these conclusions. I think there were several drivers. Critical responses to his books; evolution of the political conjuncture inside the PCF; and, if I understand this, the increasing influence of his student-colleagues, especially Macherey, all contributed. But the two main impulses were the maturation of Althusser's own philosophical tools, which he applied to himself; and the shock of the failed revolution of May '68, which led him to engage in a sustained way with the inadequacies of Marx's theories of ideology and the state. The results were a self-critical shift in emphasis and a re-formulation of some of Marx's key concepts, which Althusser came to criticize as either incomplete or just plain wrong.
It's important to stress that Althusser published little of what he wrote in these years. Some of his manuscripts were circulated among his colleagues and friends. But the French intellectual public were unable to encounter them until their posthumous publication in the 1990s; while English readers are just now receiving them. This created a significant distortion which minimized the significance of Althusser's self-criticism while failing to appreciate the full context of what he did publish. For example, his very famous essay of this period, "Ideology and Ideological State Apparatuses", one of his best-known works, turns out to be two excerpts from a full-length book, On the Reproduction of Capitalism, published at last in English in 2014. This was not known at the time. Today there are multiple texts from this period collected in book form in English: The Humanist Controversy, On The Reproduction of Capitalism, Lenin and Philosophy and Other Essays, and Philosophy and the Spontaneous Philosophy of the Scientists. But, something less than half of this material was published during Althusser's lifetime.