Core.ac.uk is added to Open Access Alternatives feature in order to improve Open Access search results. When checking for open access articles, we now query at both unpaywall.org and core.ac.uk. If we are unable to provide an open access version through unpaywall.org, we will use the result from core.ac.uk
When suggesting an open access article through Core, we provide information about it in the popup as shown below. Please note, that the text 'Open Access by Core' is configurable in the popup settings.