One thing I noticed in the UK is that there are items which are "Prime Eligible" and items that are "Delivered at no extra cost for Prime members". The latter w

One thing I noticed in the UK is that there are items which are "Prime Eligible" and items that are "Delivered at no extra cost for Prime members". The latter will also give a "guaranteed" next-day date, but seem far more prone to slipping and getting a "Now expected" date.