  The recent formulation of the factorization theorem for transverse momentum
spectra in terms of well-defined transverse momentum dependent distributions
(TMDs), allows for a better understanding of the role of the perturbative and
non-perturbative QCD contributions and their interplay. In particular,
non-perturbative effects are often included both in the evolution of the TMDs
and in the modeling of their scale-independent part. Using the available
Drell-Yan and $Z$-production data at low and high energy we show that, for the
currently available dilepton invariant mass values, the TMD evolution is driven
mainly by its perturbative contribution, while the needed non-perturbative
correction is scale independent. We then detail the difference between the
scale dependences in the high and low boson transverse momentum regime and
discuss the related theoretical errors.
