The first cel that I ever got was almost bent in 
half.  The mailman decided to bend the envelope 
in half to fit in my mailbox.  I almost freaked 
out till I opened it up.  The cardboard was bent 
in half, but the cel was attached only at the 
ends of the cardboard.  So, the middle of the cel 
wasn't creased at all, just sharply curved.  It 
eventually flattened out after a few days in my 
cel book with no signs of damage, even paint.  
Lucky me.  Later.