I'm pretty sure the only douga are sketch 3 and 
sketch 4...the rest are genga. Really nice 
considering genga is getting *really* hard (and 
expensive) to find.

There are a couple of ways of distinguishing a 
genga from a douga. 

Genga are more roughly drawn (like my 
Hotaru/Chibiusa below); they are after 
all, "concept" drawings. The yellow sheets 
are "retouch" genga and are more detailed then 
the genga done on the white sheets.

The douga; the sketch you usually get with your 
cel (and are usually stuck as well) are modeled 
after the genga. Douga have very clean, almost 
perfect, lines. They usually don't have 
any "directions" on them, maybe just some light 
shading. 

It's more complicated then what I've said. One 
could pretty much write a book over these things.