According to Osho, whether Lieh Tzu ever existed is irrelevant; the reality that matters is the living Tao-consciousness expressed in the stories. Authorship, names, even single versus multiple writers, add nothing and take nothing away. Whoever touched that vision is 'Lieh Tzu.' Value the intrinsic beauty and insight, not historical pedigree or scholarly certainty.
It doesn't matter who wrote the stories; what matters is the wisdom inside them.