It could have been produced to check a directors 
idea, were they do the scene several different 
ways to see which has the correct affect.
Or it could have "been" a affect cel that wasnt 
used at all.
Madhouse is know for trying many different 
approaches to animation, just as Gainax was.
Anyways, its still a real neet cel to have.
Also, does it have anyopther notations on it?
Like a symbol ike a star or a sun?
I have seen those as well, they indicate a 
change in lighting.