ATLASerials and CPLI do not have much overlap. American Theological Library Association and Catholic Library Association (the people that create CPLI) have an agreement that they will not index the same journals, so only the few that were duplicated in the past are in both. ATLASerials indexes only a handful of Catholic journals, so if you are trying to do a comprehensive search or one that provides a Catholic viewpoint, you should search both databases. You can search both databases at the same time! Ask me how!
...how you can ask me about ATLA Serials and CPLI (or any other reference or research question you have). Email, phone, make an appointment, stop by on a whim, leave a comment on this blog, and possibly by end of summer, IM.