Use More Than One Tool
It is important to use multiple tools, because there is no one database that indexes all journals or all issues of journals. In short, each has large coverage gaps.
In the sciences, for example, Web of Science covers just 61% of titles indexed in Compendex.
In the humanities, Scopus covers just 16% of titles indexed in the MLA Bibliography.
Within the social sciences, Web of Science covers only 38% of titles indexed in EconLit.
In addition to coverage gaps related to journals, every database also differs in terms of format inclusion. Some also include conference papers, working papers, books, book chapters, blogs, dissertations, and/or other works.
Unlike library catalogs, which practice "authority control," some database tools do not uniformly distinguish between authors with the same or similar names or pull together all publications by an author who has published with name variations. This is a problem within and between these tools.
If an author has not consistently published with the same name or exact spelling or format of her name, not all of her work will appear in a single search of Google Scholar, for example. Furthermore, her name may be listed differently within Google Scholar than in Web of Science, which in turn may both list the author differently than does Northwestern Scholars. Some platforms use first names while others use first initials or first initials and a wildcard, some may include a middle name, etc.
This issue is known as "author disambiguation" or the "management of authorial identity."