Yes, the date on the box is unopened. It should also states on the package that it's good for 7-10 days after opening. I usually finish mine off within 1 week. I've noticed that the longer you keep it open, the more the solids settle to the bottom. It's unappetizing. I prefer to limit consuming it straight out of the container (for cereal) in the five days after opening. Beyond that I use it for cooking.
The one I have is Organic Valley brand and I couldn't find anything on the carton. It's been a good 2 or 3 weeks so I'll go ahead and toss it. It was my first carton of soy milk so I didn't know if maybe it was good an unusually long amount of time. Thanks guys!