Back in 1970s, I think Kirkland (spell?) and Gerry Sports were the only companies that sold sizeable panniers in USA. I was not into touring at the time, so I can't say that with certainty, but those are the brands I recall seeing. I really wished I was rich enough to buy the Gerry panniers back then. I recalled trying to make some panniers from some army surplus bags, that was a dismal failure.
A year or two ago I bought some nearly new Cannondale Overland panniers at a swap meet (no, they are not for sale) and that sparked my interest in history at that time. I do not recall how I found this image, but found it somewhere on the internet, saved it to my hard drive. I think it was from a sales brochure.
Cannondale:
http://vintagecannondale.com/year/1985/1985A.pdf
http://vintagecannondale.com/year/1982/1982.pdf
https://vintagecannondale.com/year/1974/1974.pdf