I realize that this is an old question, not sure how it got by all of us here in the community without an answer but here you go. The Release Planning page defaults to showing the current release (based on date) plus the next two. If there are fewer than two future releases then you'll see the current release and one or two past releases.
In my subscription we always have several future releases planned so defaulting to the current release plus two works well for us. Using the carat controls to pan back through past releases isn't really relevant and we just ignore them. Hope that (belatedly) answers the question for you!