FWIW, many of the crystals used in "classical" neutron diffraction experiments were pretty elderly samples by the time data collection was initiated, partly to allow large crystals to grow ever larger, partly because of the mandatory deuterium exchange process and partly because the experiments lasted weeks to months. To be specific, I believe the crystal that led to the first endothiapepsin neutron structure was 11 years old before it began D2O-soaking prior to the neutron experiment. It diffracted pretty well, 2.1A I think...
Cheers- Brad
