As long as its completely sealed it wont really hurt it. But if not it will pick up moisture and it wont smoke that well.it doesnt have to do with glycerin or honey IMO. its just that it picks up moisture and you really dont want water in your shisha.
AS for keeping it fresh. well all am going to say is "are you going to chew it??" Its dried tobacco leaves with added molasses. Its not fresh when you buy it. We just call it fresh if its production date is recent. Its the same as saying my car is fresh :P lol