Now I know no one believes me, but I saw this on AMW (Americas Most Wanted). You can date a garment by the ILGWU tag.
It said that you have to look at the last 2 numbers on the back of the tag and that was the date. They called and this is what they were told. You can follow the link below and it takes you to the page of the investigation. If you scroll to the bottom you will see it. The 2 numbers above the long row of numbers means something too, probably the month but usually we can't see that part of the tag unless we take a seam out. Now take this for what its worth, but this is what they said, I'm not making it up!