The extensional-flow data of Huang et al. [Macromolecules 2015, 48, 4158] of several polystyrene systems are here successfully compared with predictions of a recent model of Ianniruberto [J. Rheol. 2015, 59, 211], provided flow-induced friction-reduction effects are accounted for. For the case of solutions, friction reduction must include nematic interactions between the oligomeric solvent and the polymer molecules. It is here found that the coupling interaction parameter epsilon must be larger than that based on the mean orientation of the solvent molecules, as measured in mildly oriented systems; the larger e found here is probably due either to the stronger orientation reached in the extensional flows, or to the fact that only the molecules close to the polymer matter in frictional effects. The model here suggested is the first multimode molecular model (aside from simulations) able to describe, qualitatively and even (almost) quantitatively, the nonlinear extensional rheology of entangled polymers, from melts to solutions.