Depending on the animation itself, there can be
over a hundred cels in a sequence, it's possible
they're direct sequencemates, like A44 and A45,
where the differences are very VERY slight.  Oh,
and name the series please.  It's hard to identify
fraudcels, except to say the artist painting them
isn't always perfect, or a shade might be off. 
Compare to a screencap.