A very small number of stretch goals unlock add-ons that are purchasable but not included in the Survival Box. (Map Pack 1 is the first example.) This is because we have to plan the Survival Box cost to you based on both the launch value and the final value if everything is unlocked. Including the small number of premium add-ons that we might unlock with stretch goals would have raised the initial cost of the pledge level to a point where it would not have been worthwhile at launch. (We did the same thing with the High Lord Miniatures in the first Kickstarter.)
We make efforts to ensure that we add real value to the Survival Box even without these premium add-ons, through full product additions like the Booster Deck and Delphi Missions book (and more to come).
As far as the wording goes in the description - we cannot change the description after the campaign has launched. We chose the wording as it is because any description that referred to "some stretch goals" would have been confusing before the few exceptions were revealed. We will always be very explicit with the stretch goals and add-ons so that you know when an exception appears. And otherwise we will continue to add many more items to the Survival Box so that its value only continues to grow.