They can use same image, but would mean creating 4x icons in the crafting screen. There are other crafting cases that are similar, like levelling up trauma kits / explosives levels 1 -> 2, 1 -> 3, 1 -> 4, 2 -> 3, 3 -> 4. I get that it's not exactly the same, but was thinking along the lines of reducing clutter in crafting.