Hello!
I had the same problem with an otherwise lovely 
Ryo-ohki toddler cel. ;_;
It is HUGE!! But the image area is relatively 
small. There is a large crease in the cel that 
would be trimmed off...
I /could/ trim it to a normal size, and lose no 
image at all!
Then it would fit into my regular celbooks and...
Ahwell, I know I'm not going to do it, even though 
 it has obviously already been trimmed before.
Why? Because it would trim off the all-important 
sequence number and registration holes.
Even if you never intend to sell a cel, one day 
things might change, or someone might offer you 
the perfect trade, or... well, any of a number of 
things.
At any rate, I know your angst! Stay strong, get 
an oversized celbook and remember that we don't 
really own art, we just borrow it.
Cheers!
Ryo