Yesterday while visiting John and Linda Lipman we tasted a Old Grand Dad Bottled-in-bond from a bottle from the 1950's (tax stamp faded and blurred but we think bottled 1958) against the modern product. Here is what I remember.
Color: The National version was darker and probably older.
Nose: The national had a nice pronounced caramel and clove spiciness with a hint of fruit. The Beam was very similar but not as pronounced or deep.
Taste: The National was very sweet with caramel and sweet spicey clove and apricots with just a hint of oak wood and smoke. The Beam was very similar with caramel and cloves but the fruit was just barely on the palate there was a little more oak wood.
Finish: They both had a very nice sweet caramel and spice finish that lingers for a short while.
I would say that Beam has done pretty well by this brand and the mash bill is probably the same, but they are cutting corners with a higher barrel proof and less age.
Mike Veach