I'm not sure about them being S-Rank, because I don't see them on the page. But it tells you how to get them right on top of the page.
Unlike the previous games, Ranger: Guardian Signs has a mode set in the past. This mode has you needing to find Pokemon by collecting Litographs after capturing them. These Litographs have a small of appearing so you have to be observant. The Pokemon in the past are catalogued in a completely different manner to in the present. This page is to catalogue all the Pokemon in the past browser as well as give you their location in the past. When the Pokemon are your partner, you have the ability to bring them to the present with their Field Ability at 1. The Pokemon listed as being obtainable from are the ones you need to defeat in order to get the Litograph for this Pokemon.