One of the features in the legacy catalog, Socrates, but missing in SearchWorks, was the ability to search for a series in the "basic search." I am pleased to report that this is no longer the case.
SearchWorks now offers searching by series in the simple search using the pull-down menu.
To see how this works, try searching "Collection de documents inédits" as a series - this brings up the individual titles in the "Collection de documents inédits sur l'histoire de France" (as well as titles from several other series with similar names like the "Collection de documents inédits sur l'histoire économique de la Révolution française."). To bring up the record for the entire series, you can search the series as a title, but the record is too general for most needs, it notes that the titles are cataloged separately. Some journals which have many issues with thematic titles are also cataloged in this way, for example Yale French Studies.
Some of the other important series that may be of interest include:
Textes de la Renaissance
Collections de l'école française de Rome
Civiltà letteraria italiana
Manoscritti datati d'Italia
Many scholarly works in both French and Italian are published in long series. Works published by scholarly associations or university departments are some examples, or by major publishing houses, such as the various series entitled "Storia d'Italia."
FYI : Unfortunately there still exist some series whose cataloging is inconsistent, with some titles not being cataloged separately, and others listed in the catalog as separate titles but without a series. But if you are stuck, sometimes it helps to search by series.