We have had an emerald crab for 3 - 4 months now and have yet to see any evidence of molting. We had a Sally Lightfoot for a short time and it molted twice. Even the cleaner shrimp has molted twice since we got him about two months ago.
I've seen a molt from mine... they need proper calcium levels to molt.
The one I have now for the last few months hasn't grown/molted, but the one I have before molted a few times. What's proper calcium level? Dunno.