Hi pete
I am a but slow today and this is not so clear for me. What exactly were you trying to accomplish? It seems to relate to some pre-existing torrent/files rather than new ones right?
What exactly do you mean ...
when I add a transfer that files are already completed in download location, Tixati won't recognise those files
By 'transfer' I assume you mean a .torrent or magnet link right?
By 'download location', do you mean the folder for incoming files, before they are finished and moved to the completed/seeding location? Or was an attempt to add a torrent/transfer that was already completely finished, just loading it for seeding purposes or ?
For the torrent/transfer you tested, were some files complete and others not finished?