This is a pic of the upper eye of the shock where the adjusters are. You have to fully turn in the adjuster to allow the upper spring retainer to fit over it. The one on the left is fully extended while the one on the right is fully turned in.
You can see that groove there on the base of the shock's head. A retainer ring slides into that groove and allows the upper spring retainer to rest on it and not fall out.
That retainer ring is in the bag that is next to the shock in this picture.