What is the difference between quality control and a proofreading project?

A proofreading project is launched by a client into a single language: the target one. The proofreader does not have access to the source text and has to proofread the target text to ensure that it is fluent in their native language.

Quality control is performed by a Language Manager, who checks the quality of the author's work. The Language Manager has access to the source and target texts and can rate the author.