If you pull the list up on the UMD of Baltimore bookstore site, there are a more items on the list. I think it's just because the Baltimore bookstore has more items in stock.
There is even an extra book that is "required" that came up on the Baltimore list.... for SG1 students. I too will be attending the shady grove campus, I just happen to pull the list up on the umd bookstore site and noticed the difference. **Makes things more complicated than it needs to be. But oh well.