What does Barns n Nobles do to all the old magazines? And how often do they throw out the stuff?

Often old magazines are returned to the publisher to be pulped, or kept and sold as back issues.What does Barns n Nobles do to all the old magazines? And how often do they throw out the stuff?
I worked for a drug store that got their magazines delivered by a company called Charles Levy. CL would have a rep come in once a week and change out old magazines for new, and then a truck driver would come another day that week and pick up the old and bring new again. I assume the mags went back to CL and then they sent them back to the companies.