One way that helps me date a garment is with the RN number.

What is an RN number? 

An RN (Registered Identification Number) is a number issued by the FTC, upon request, business residing in the United States that is engaged in the manufacture, importation, distribution, or sale of textile, wool, or fur products. (FTC.gov) In other words, an RN number is an ID for a clothing brand. The number correlates when the certain brand began.

When you find an RN number, you can look for it in the database here. However, this is only accurate for those numbers issued after 1998. If you believe the garment is older than 1998, then this calculator will help.

In 1956, the first RN number was given of 13670. This calculator will help identify the year that the RN number was issued. The calculation does NOT tell you the date the item was made. It does tell you the earliest the item was made. For more information click here.