HowNet is an authoritative database for collecting papers. All the papers collected by HowNet can be retrieved on HowNet. A piece of paper can't be found for a while, but it may be found for a while.
HowNet is a common paper duplicate checking system. When you check, articles similar to yours are not included. When you check it again after a while, you may include articles similar to yours. Even if the test paper has not changed, different duplicate checking results may appear.