Welcome to NC
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I too unsnap prior to washing. As for the use of boosters - it's a try it an see type thing. After using MCN for so long now, I can just tell if a nappy is going to be ok with my boys or not, by knowing how many layers of absorbancy are in there to begin with.
You'll find on average nappies have around 6 layers of absorbancy for day use....I wouldn't use anything less personally.