If you look over the whole car, mounting holes for everything, nearly all have oversized holes and/or oval holes for adjustment. Its not a myth, tolerance stack up from front to back could be up to 30mm, someone had a sheet once that showed how much it could be out when replacing panels at Vaux bodyshops. I know on some modern cars (specifically a high end car manufacturer) BIW tolerance is 26mm from datum to rear of vehicle... even nowadays with all mod cons....