Original sentence: Retro Hugos were awarded 50 years after years in which World Conventions didn't give awards — note: no "Best Novel" Hugo was awarded at the 1957 convention, but Hugos were awarded in other categories, hence there was no "Retro Hugo" for 1957 awarded in 2007
Edited sentence: Retro Hugos were awarded 50 years after years in which World Science Fiction Conventions didn't give awards — note: no "Best Novel" Hugo was awarded at the 1957 convention, but Hugos were awarded in other categories, hence there was no "Retro Hugo" for 1957 awarded in 2007