works

The plugin does not affect what search engines do. It just changes the look of the 404 pages to help your visitors with a user friendly page in case of an 404 error. The 404 code is not changed which differs from other plugins. Code 404 means that the requested page does not exist. If a search engine has indexed a page and you delete if for any reason the search engine will remove it from the index after a while due to the code 404. This is the normal behavior and it is not changed by the plugin.