First of all, the papers that have not been included in HowNet mean that these papers have not been reviewed and included by HowNet, so there is no relevant information about these papers in HowNet database. Papers collected by HowNet need to go through strict academic review and editing process to ensure their quality and originality.
Secondly, the duplicate checking system of HowNet detects plagiarism and duplication by comparing with the existing literature resources. If a paper is not included in HowNet, it can't be checked again.
In addition, HowNet's duplicate checking system mainly focuses on the comparison of text content, and its duplicate checking ability is limited for non-text elements such as pictures and tables. Therefore, even if a paper is not included in HowNet, if its elements such as pictures and tables are similar to other published papers, it may still be detected by the system.
To sum up, papers that are not included in HowNet cannot be searched by HowNet. If you want to check the duplication of such papers, you can consider using other duplicate checking tools, or submit the papers to relevant institutions for review and inclusion. At the same time, the academic community should also strengthen the supervision of unpublished papers, improve the awareness of academic integrity and maintain the healthy development of the academic environment.