Is dark energy meaningless?

We show that there are isometrically nonequivalent Robertson-Walker metrics which have the same set of geodesics. While one of these metrics satisfies the Einstein equations of pure dust without a cosmological constant, all the other describe pure dust with additional energy momentum tensor of cosmological constant type. Since each of these metrics have the same geodesics it is not clear how to distinguish experimentally between the Universes whose energy momentum tensor includes or not the cosmological constant type term.