Absolutely correct. The architectural use is actually closer to what conservative and Christian thinkers meant by the passing of "modernity." Tom Wolfe's From Bauhaus to Our House was a humorous and satirical treatment of the excesses of architectural modernism and minimalism. When the fads no longer worked to hold aesthetic attention, it was necessary to return to elements from older forms - classical, Georgian, Federalist, Tudor, Gothic, etc. We're still in the "revivals" and "postmodern" synthetic experiments now. Although...outrageous examples of "modernist" architecture are still unloaded on the public -like LA's monstrous new cathedral.
I seem to recall that Arnold Toynbee uses the term "Post-Modern" in A Study of History. The political theorist and philosopher of history Eric Voegelin talks about "modernity" in his 1951-1952 book The New Science of Politics . Guardini had been writing similarly in the 1940s (The End of the Modern World). What "postmodern" tended to mean around that time was the collapse of the secular hubris of the modern age and many of its idols, particularly a belief in unending social progress centered on modern liberalism, the modern nation state, and the various classes who had placed their hopes on science and technology while abandoning Christianity. The "postmodern" was then the period of reconfiguration and the social and cultural processes at work at sorting out these issues.
How the term was hijacked to signify the bizarre ideologies of skepticism and relativism in literary criticism and cultural theory is a strange episode in the history of ideas. It leads to a great deal of incoherence and equivocation in academic discourse. For the most part it is a circular discourse which has meaning only for French literary Marxists and their internal dilemmas. How it became a dominant discourse and ideology in American academia is quite bizarre in the extreme, although it answers to certain liberal fantasies.
I should add that there is an internal contradiction involved in claiming that essential or foundationalist knowledge is impossible. The claim itself involves just such a metaphysical assertion - "I have certain knowledge that certain knowledge is impossible." I think Derrida even admitted the contradiction but seemed to think this was an even deeper and esoteric mystical insight. Bizarre.
None of the left-wing books I have seen from the movement even come close to the proper form for framing a scholarly discussion on the pros and cons of moral relativism and epistemological skepticism. They are exercises on rhetoric, propaganda, and literary allusions.
In terms of left-wing "postmodernism" as an ironist skepticism, John Kerry's "I actually voted for the war before I voted against it," is a good example. Derrida, Foucault, Lacan, Baudrillard, Habermas, Lyotard, Jameson, and Eagleton could each have written 700-page volumes explaining the hermeneutics and deep significance of that proclamation. Although perhaps Umberto Eco could do it more poetic and symbolic justice.
"I have certain knowledge that certain knowledge is impossible."
This is as old as the hills and is what separated the ancients from the moderns. So, three positions: ancient, modern, post-modern. My guess is that most people's laconic dismissal of French chic is not sufficient enough to qualify as modern or ancient.