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Evap vent valve normally open - fuel vapors don’t leak out?

I’ve been reading up on general evap system operation and apparently the canister vent balance is normally open to the atmosphere and closes during leak testing and when vapors are being pulled into the engine for burning.

So my question is, if it’s normally open to the atmosphere and fuel vapors are stored inside within the charcoal... do the fuel vapors not escape out to the atmosphere at all?