Well this is what i have learned from my time in 
this hobby.  it may sound dumb but it works a 
little for me

sometimes, there is more to a cel then what is 
shown on TV.  usually cels have about 1 to 2 
inches more artwork around them. (the rest of a 
body or more hair ect)
I have this inuyasha cel as an example. 
inside the border is what We might see on TV and 
not the rest of the cel.

Sometimes fancel artist will just copy what they 
see on TV (unless they have the REAL cel).