But plenty of philosophers prior had suggested, if not argued, the contigency of knowledge. Kant famously discussed how knowledge is shaped and circumscribed by our faculties (e.g. sense of space and time).

Positivism was already well developed long before 1963.

I could on. I've studied enough philosophy to be comfortable with my criticism. But I'll grant that it may not have been until after 1963 that all these philosophical strains became predominate. But that doesn't excuse people from not seeing what's coming.