Our contact at the The Filson Historical Society told us...Mammoth Cave bourbon became a brand **** by W L Weller and Sons about the year 1900. They were of course buy whiskey from other distilleries at the time, but one of their main suppliers was A. Ph. Stitzel Distillery in Louisville. As a result they ended up investing in the distillery and by the time that prohibition started Stitzel was the president of the distillery and Secretary/Treasurer of W L Weller and Sons, Alex Farnsley was the Vice president of both companies and Julian P. Van Winkle was president of Weller and Secretary/Treasurer of Stitzel Distillery. The result was Weller was able to piggy-back on the Stitzel license to sell during prohibition and Mammoth Cave was one of the bourbons offered for to pharmacies during this period.
During prohibition, no distillery could distill whiskey until 1928 and even then it was limited amounts. The result was that many brands, such as Mammoth Cave, were supported by purchasing whiskey for distilleries without a license to sell for "Medicinal Use". That is the distillery that made the whiskey that became this Mammoth Cave bourbon.
Our contact has seen several bottles of this bourbon in the past and the United Distillers archive had about a dozen or so bottles in the collection. They actually opened a bottle and tasted the whiskey and tell us, "That bottle is quite good."