...oftentimes, someone, maybe even the studio, 
paints -on top- of the cel itself...which creates 
dicoloration and just looks generally bad.

Also, I have many cels with the thin pen writing 
the sequence number...it just means that's what 
the animator hadon hand.

Plus, it's not a close-eyed "primo" shot, and 
while (I'm assuming) it is bank, if someone were 
to make a fake cel, it would be of a more choice 
part of the sequence, perhaps with open eyes or 
whatnot.

Just my two cents...

-Misha