If the shortest distance between the lines \( \dfrac{x - 4}{1} = \dfrac{y + 1}{2} = \dfrac{z}{-3} \) and \( \dfrac{x - \lambda}{2} = \dfrac{y + 1}{4} = \dfrac{z - 2}{-5} \) is \( \dfrac{6}{\sqrt{5}} \), then the sum of all possible values of \( \lambda \) is:
