I have found that in both of my baby snows, its hard to tell when they are in shed, i have once noticed the eyes on my male milky, have had then both for about 3-4 months and have had 2-3 sheds each, usually i just find the shed in they tubs afterwards.
funny you should mention this; i got a grown on motley amel the other week which is settleing fine, feeding like a gannet and as gentle as they come. on sat (the day after feeding) i went to her cage to find a freshly shed skin. shocked me at first but there you go. I geuss people were right when they say "always expect the unexpected"
The best way to tell is the colours, you will notice it looking dull then the eyes start to cloud, even with snows. I can even spot it in my blizzards. The eyes will clear and the colour return slightly for a day or two then you will get your shed. The mood thing is quite normal during ecdysis(shedding), it's just uncomfortable for them, and i think they probably feel insecure due to their hindered eyesight. Hope that helps.