I think the best QC can do is keep double checking everything occasionally make "tests" to assess the project. This can be in many forms, like just some questions that express our concerns about the product,  or asking about a thing that you do not understanding why they are doing so. Theses can all be signs that the procedure/product needs verification. I think it works bests if a QC follows the production in a timeline manner and do the "quality control" work by ticking boxes for each stage: investigating each stage of the production carefully and make sure that it is going in the right direction for every step.