Black powder, when stored correctly, doesn't expire. I'm using some 1f that my father use to use in a pipe gun he made in the 50's.
Here's how to read the manufacture codes on the bottom of the can:
The code on the Goex can gives the granulation, the lot number, and the date of manufacture.
For instance: 02/73.00NO3B
From left to right, this breaks down as 2f granulation, lot number 73. It was manufactured in the year 2000, the month of November, on the third day of the month, and packed on the second, or "B" shift.