Objects appear dynamically

If I understand well: when the user gets to a slide, without starting from the summary slide, the Back button shouldn't appear on that slide?

You will have to track the item that is clicked on the summary slide, by using a Boolean (user) variable for each item. Set its value to 0 with the On Enter action of the Summary slide. Setting the default value only to 0 will probably not be a good idea, because the user can come back to the summary slide, without clicking on any item and proceed that way. Could explain more if you didn't understand. You'll need those actions (after creating all the needed user variables, one for each item):

• For the On Enter event of the summary slide this Standard action:
      Assign v_1 with 0
      Assign v_2 with 0
      Assign v_3 with 0
    .....
• For the items to be clicked on the summary slide, use a shared standard action like this:
      Assign v_1 with 1            define the variable v_1 as parameter
      Jump to slide_one          define the slide as second parameter
• For the On Enter event of each slide where a Back button should appear I would use also a shared conditional action
      IF v_1 is equal to 1                  v_1 is again a parameter
          Show Bt_Back1                     Bt_Back1 is the second parameter (if you have an individual back button)
      ELSE
          Continue