For fun I looked up the term in google books. The earliest use I found is this:
Oddly (seemingly) it is used in connection with Calvert whiskey (circa-1960) to explain why its Extra blend, still sold I believe, has a particularly soft character. I wonder what element of Calvert Extra was made in a small batch. Was it the straight whiskey component? If so was it a pot still product? The term small batch can mean the latter in distillery terminology (sometimes termed "batch whiskeys"). Or was it the neutral spirit element? Anyway I was surprised to see the term used in a way quite different to how it is understood today. Perhaps they simply meant that small batches were prepared of the usual Calvert blend to get the best results.
I wonder what those 22,000 experiments were all about? That's a lot of experiments. Jim will have to keep SB going a long while before I or even those who have exceeded me in posts will ever get to that number..