Profits from operations are used to support a wide variety of university and student activities. Discontinued books are shipped to a wholesaler who recycles them to other colleges and universities where they are needed.
Old editions have no national value.
Recycling your books is good for the environment and lowers the price of textbooks. Books with writing or highlighting may have value. The faculty's continued use of a book helps determine it's buyback price. Wholesale prices are based on national supply and demand. Copies in poor condition will be reduced appropriately.