Publishers love series because they believe that readers love series. And they're right, it would appear. This presents certain complications to serious readers who want to fully enjoy their reading. Most of us want to read the series in order. This can be difficult when you don't know what books have appeared in the series and what the proper order is.
Publishers are notorious for listing the author's other books out of order.
Authors further confuse things by occasionally writing the books out of order, going back to fill in earlier events in later book, for instance. Never fear, resources are at our fingertips to help us through these difficulties. A number of reference books provide series lists, but they are hard to find and go out of date fairly quickly. I'd give you the details if I had them, but I don't. I can, however, help you use Web to solve this problem.