  A factorization hypothesis is tested by examining a form factor of the
$\omega\pi$ production in hadronic $B^0 \to D^{\ast \pm}\omega\pi^\mp$ decays.
The form factor is compared to that from available $\tau$-lepton as well as
$e^+e^-$ data using the conserved vector current hypothesis. The difference of
normalizations of form factor shapes from $B$ and $\tau~(e^+e^-)$ data
indicates the important role of the large $N_c$ limit in QCD. Moreover, the
growth of the difference between the form factors with the $\omega\pi$
invariant mass is related to the perturbative QCD corrections of factorization.
The current precision of $B$ data does not allow one to find any evidence of
corrections to factorization. A promising study could be performed with the
Belle II and LHCb data sets.
