Attaching facing to lining

I'm having a (conceptual?) problem attaching the facing to the back lining. The length of the outer curve of the facing is about 6 cm longer than the curve of the lining neck, and I expected them to be the same length since the instructions say to first match the outer edges. Am I misunderstanding the instructions for how to arrange them? My pattern pieces haven't become distorted - I checked them against the paper pattern.