Many breweries stamp a number on the can or bottle that signifies the day number of the year, some are 5 digit numbers with the last 3 digits being the numerical day of the year that it was bottled! for instance 19324, meaning that it was bottled on the 324th day of the year! So there is a reference as to how old or how fresh the beer is! Firestone Walker stamps bottled on dates right at the start of the neck on their bottles and is very hard to see unless you hold it up to the light but it is there and many other breweries do this as well! The problem is that the print is so small and hard to see that many of us never know that its there!