If I may ask a question please, seeing as its your creation..

When downloading covers/metadata..

as an example 100 books - you get to 50 and need to quit the program for whatever reason or calibre crashes because of something I'm doing in the background.

Where does the partial data go is there a way of using the say 50/100 that has already been downloaded/scraped or is it simply restart from scratch?

Regards and thank you for your time and Calibre...