Just a lame question about key cels.

Sometimes I come across a cel and matching sketch 
where the number/letter on the sketch is circled 
(i.e. "A8") but the letter/number on the sketch 
itself isn't circled.  Does this mean the sketch 
is a key sketch but the cel isn't?  Or are they 
both considered key elements?  I'm asking, 
because if the cel were ever seperated from the 
sketch, you'd never know.  Just curious, and if 
anyone knows I'd appericate a response. Thanks in 
advance!

Van
Trowa.com ///.-