I too, despite having great recall, have issues recalling the details of a DCs face. I think this is due to interference from our left brain. The left brain associates "symbols" to things, such as facial structure. This is why so many people have issues drawing because when you draw an eye you draw an oval shape with a circle in the middle, as is the symbol from your left brain. In actuality, each eye is very different.

I'm still not too great at remembering what DCs look like, but I found the best way to get as much information as possible is to study the finer details of their appearance, as you would if you were attempting to draw somebody's portrait. And instead of noticing their eyes as eyes, notice them as simple shapes, lines and how wrinkles look as they're hit by light.