I do the same thing. I go back & check the show 
to see if I can find the exact cel. I tend to 
lean towards cels from moments in the show that 
mean something to me.
  I check my other cels because on some 
characters I don't necessarily want a dozen cels 
of that character. If this is the case then I 
decide do I like the ones I have more than the 
one for sell.