We discuss our recent study of the impact of collinear PDFs and their
uncertainties on the determination of transverse momentum dependent (TMD)
distributions and the description of Drell-Yan (DY) production measurements
at low transverse momenta. Using QCD factorization and evolution in transverse
coordinate $b$ space, this study takes into account for the first time
flavor-dependent non-perturbative $b$-profiles. It illustrates
that collinear PDF uncertainties and non-perturbative TMD flavor dependence
are both essential to obtain reliable TMD determinations.