Aston Martin’s IPO will provide further clues to which category ultra-expensive carmakers really belong.
its context:economist
Grammatically,you need to have " clues to which..." and " to which... belong ". So is "to" double duty here?
Or it should have been:
Aston Martin’s IPO will provide further clues to which category ultra-expensive carmakers really belong to.
Do you think it is acceptable or the writer made a mistake?