  Web of Science Core Collection, one of the most authoritative bibliographic
databases, is widely used in academia to track high-quality research. This
database has begun to index online-first articles since December 2017. This new
practice has introduced two different publication dates (online and final
publication dates) into the database for more and more early access
publications. It may confuse many users who want to search or analyze
literature by using the publication-year related tools provided by Web of
Science Core Collection. By developing custom retrieval strategies and checking
manually, this study finds that the "year published" field in search page
searches in both online and final publication date fields of indexed records.
Each indexed record is allocated to only one "publication year" on the left of
the search results page which will inherit first from online publication date
field even when the online publication date is later than the final publication
date. The "publication year" field in the results analysis page and the
timespan "custom year range" field in the search page have the same function as
that of the filter "publication year" in search results page. The potential
impact of the availability of two different publication dates in calculating
bibliometric indicators is also discussed at the end of the article.
