When i import a nzb and delete the headers after downloading, then when I import them again, it shows the (deleted) headers again as new files

So now I dloaded 20 files for the second time from a payserver and I prefer not to compare each file manually to see or I dload it the day before.
Is there somewhere a option to hide already deleted headers in the import folder on import? Or can it be added?
btw I need it because sometimes newzbin is not complety the first time I download the nzb headers.
Thanks