This bourbon was distilled at the Pennco Distillery in 1974 (in Schaefferstown, Pennsylvania -- not long after this was distilled, the distillery was purchased in foreclosure and renamed Michter's).  Adolf Hirsch, a former Schenley executive, had commissioned the whiskey to be distilled.  It then aged until 1989, when the distillery was once again in foreclosure.  Hirsch then sold the whiskey to the Hue Family (Kentucky) in 1990.  Although most of the stock was transferred into stainless steel tanks (which halted the age at 16 years, see A.H. Hirsch Reserve 16), some was further held in barrels and bottled at 18, 19, and 20 years. 

For more info see this Chuck Cowdery blog entry.  

This legendary bottling turns out to be, yes, extremely tasty and dangerously drinkable on top of that. A mildly-sweet number (meaning there's a tinge more sweetness than I'd expect for 20 years) that pleases without being very complex, and with a richness that's satisfying without being overwhelming.

And that's the extent of my notes, because it's all I managed to jot down while I was overwhelmed by the excitement of discovering a mostly-full bottle of this on the backbar of a restaurant somewhere in the Rocky Mountains. This botle had no right to be there anymore, so of course I drank as much of it as I could... but I left some for you... if you find it!  B+/A-