The files associated with add-skip function are not deleted when your delete the recording. There is a clean-up routine that runs every night which is supposed to remove the files. Not sure if it is activated at the moment. Kodi only shows directories in "Recordings" that have either a *.ts or *.mkv file - the recordings themselves.
The cleanup is prevented "around" the time that recordings are scheduled, so if you do a lot of recordings overnight they may not be deleted.
The cleanup is prevented "around" the time that recordings are scheduled, so if you do a lot of recordings overnight they may not be deleted.