As explained at sku's site
Example 1: K0780907:21
Example 2: N3001114:13
The first letter is the bottling line at Buffalo Trace; example 1 was the K line, and example
2 was the N line. I don't know enough about the bottling there to know if there is any real
significance that can be gleaned from the bottling line.
The second three digits indicate the day of the year that it was bottled. So example 1 was
bottled on the 78th day of the year and example 2 was bottled on the 300th day of the year.
The third two digits indicate the year - this is really the most significant piece of information.
The "09" on example 1 indicates it was bottled in 2009, so if it's Pappy 15, it would likely be
from the old Stitzel-Weller stocks. Example 2 has an "11" which indicates 2011 when they
started using Buffalo Trace bourbon.
The final four digits are the bottling time on a 24 hour clock, so example 1 was bottled at 7:21
am and example 2 was bottled at 2:13 pm (14:13).