  We explore the effects of neutrino and electron mixing with exotic heavy
leptons in the process e^+e^-\to W^+W^- within E_6 models. We examine the
possibility of uniquely distinguishing and identifying such effects of heavy
neutral lepton exchange from Z-Z' mixing within the same class of models and
also from analogous ones due to competitor models with anomalous trilinear
gauge couplings (AGC) that can lead to very similar experimental signatures at
the e^+e^- International Linear Collider (ILC) for \sqrt{s}=350, 500 GeV and 1
TeV. Such clear identification of the model is possible by using a certain
double polarization asymmetry. The availability of both beams being polarized
plays a crucial role in identifying such exotic-lepton admixture. In addition,
the sensitivity of the ILC for probing exotic-lepton admixture is substantially
enhanced when the polarization of the produced W^\pm bosons is considered.
