I find that papers reference Raymond Cattell suggesting 16 or 22, etc, traits, by factor analysis (basically regression), including all five of the modern reproducible traits (openness to experience, conscientiousness, extraversion, agreeableness --- he called it Independence --- neuroticism).
But there is such a flood of publications by Cattell and other workers in this field, most of them applied, not theoretical, that it is is not obvious what the earliest publication containing all five of these factors was.
Tupes and Christal were the first, it seems, to be able to reproduce with a larger data set the only five factors that are reproducible, but what is the earliest publication by CATTELL that includes all of these including the other dozen or so nonreproducible ones?
What I found by Cattell is a 35 trait paper from 1947 that has all of these. Is there anything earlier? He worked in the 30's and 40's.