When cleaning out an old house, I came across some older unopened bottles of whiskey. They are common brands like J&B, Dewar's, Jameson, and Glenfiddich. I'm curious to find out how old they are. Many of them have paper bottle stamps across the top, some of which are marked "Bureau of ATF" and others marked "US Internal Revenue". I can't find anything on any of the bottles which is easily identified as a date, though there are some numbers along the side of the bottle stamps which look suspiciously like a 2-digit year along with other information (like "NY - I - 68" or "Import No. 4 - I -75"). Does anyone know when these bottle stamps were used? Any idea of how to tell how old the unstamped bottles might be?