I just bought 2 sets of tires

Not at all, what is your concern?

Roy

DOT code

In the United States, the DOT Code is an alphanumeric character sequence molded into the sidewall of the tire for purposes of tire identification. The DOT Code is mandated by the U.S. Department of Transportation. The DOT Code is useful in identifying tires in a product recall.

The DOT Code begins with the letters "DOT" followed by a plant code (two numbers or letters) that identifies where it was manufactured. The last four numbers represent the week and year the tire was built. A three-digit code was used for tires manufactured before 2000. For example, 178 means it was manufactured in the 17th week of 8th year of the decade. In this case it means 1988. For tires manufactured in the 1990s, the same code holds true, but there is a little triangle (?) After the DOT code. Thus, a tire manufactured in the 17th week of 1998 would have the code 178. In 2000, the code was switched to a 4-digit code. Same rules apply, so for example, 3003 means the tire was manufactured in the 30th week of 2003.

Other numbers are marketing codes used at the manufacturer's discretion.

Many automakers recommend replacing tires after six years, and several tire manufacturers (Bridgestone, Michelin) have called for tires to be removed from service 10 years after the date of manufacture

The DOT code usually consists of four digits. The week and the year is how it breaks down. An example would be: 3010 is the 30th week of 2010. Having said that, you may be looking at something other than the date code.