If it is a free span that won't ever see weight, then the nosing like you installed on the shelves will be fine. If you're going to put any kind of weight on it, then increase the height of the nosing. If the weight will be significant, then install support front and back of the shelf, the back support that will be unseen can be made of plywood. The type of support will depend mostly on the total weight upon the shelf and the amount of space you have for supporting of the shelf.