I don't think there's any other way for a crab to grow.
I bought a dozen blue-legged hermits just a few days ago, and one of them molted (I think) within hours of going into his (her?) new home. I'm pretty sure it was a molt, not a mortality, because there were no shells to spare in the tank, no immobile shells, and that shell was moving the next day.
You definately need some transition shells.My crabs started killing each other for the shells.after i put in emptys the killing stopped and all is good now.