OK this may be down to your settings in File locations.
Having created a plugins folder in the My PSP folder of My document and With both enabled and use sub folders checked. Al that left to do is Copy/Move the 8Bf folder there or in the case of Filters with installers Point to that location. Do Not add each filter as a new location if they are sub folders and sub folders Is Checked as that results in PSP not seeing them. The reason the PSP Effects Plugins can still display the names of filters that have been removed is because they are still In the cache file for plugins and Thats not been updated.
You can delete the cache file In Corel >a pp date and it will be rebuilt The next time you open PSP Its exact location will depend on your version of Windows. Doing file locations cache should show you the Path.
You can also delete from inside PSP by doing File > Preferences > Reset Preferences. and checking the box for delete Cache.