Hello
When you import a book it will get “Imported” label instead of import button. If you repeat the search and it’s shown again you will still get the label and there won’t be button to import because it’s already added.
However, this currently works only during one session. The plugin is built as a single page application so when you reload the page it will lose its state and it will not notify you about books which are already imported.
I will look into adding this option in next update
Best Regards