We study the propagation and decay of resonances, produced coherently on nuclei and decaying strongly into typically three-body final states. The A-dependence of the total production cross section is analysed in terms of the effective total cross section, σ2, for the interaction between the produced system and a nucleon. We find that σ2 becomes mass dependent, since energy conservation is not instantaneously established. This feature is qualitatively supported by a large amount of experimental data. However, this in no way proves that resonance production is the dominant production mechanism, but rather that whatever the mechanism is, energy conservation is not fully established until the produced system has left the nucleus.
