Using molecular dynamics simulations and a variant of our primitive path analysis algorithm, we have measured the total stress as well as the connectivity stress contribution for a large variety of generic bead-spring model polymer networks. For randomly cross- and end-linked networks the inferred entanglement stress contribution is excellent agreement with the predictions of the Rubinstein-Panyukov slip-tube model (Macromolecules 2002, 35, 6670). For networks undergoing further cross-linking and bond-breaking in the strained state (chemical aging), the observed stress-strain behavior can be described by a generalization of the slip-tube model in the spirit of Tobolsky's independent network hypothesis. The stress-transfer between independent networks during postcuring appears to obey unexpectedly simple relations.