They don't molt fully because they do not molt their wing feathers they loose the neck feathers (which are not really feathers before molting their)Goslings molt about 4 weeks after their fully feathered from the fluffy stage and brown or grey or buff coloured will look a lot darker.
You will not notice the white type goslings molt only on the neck and the lavender. coloured goslings will loose the grey colour and replaced by white type feathers but if you are lucky the the lavender. feathers stay