Hi,

First you received very many cels very cheap, 
so the value has been stated. The sketch will 
not make that much of a difference IMO. 
However cels that are not stuck to the sketch 
tend to be more attractive to a buyer, if you 
intend to sell them.

My Idea:

Next is a procedure that I have used and has 
worked 80% of the time:

Stuck Sketches:

If they are really stuck, then you will damage 
the sketch most likey. Whatever you consider, 
remember that the cel is the important part. 

You can "freeze" the cel in a freezer that is 
large enough to lay the cel flat. After at least a 
few hours or so, you can try to gently tug at the 
sketch. This helps to solidfy the paint, but you 
have to be careful not to have "chips" .

If it is not on too strongly it will come off easily.
If the sketch is still giving you problems and
If it is still pretty much glued on strongly after a 
days worth of freezing, I would suggest a 
different approach. Remember, that the most 
important thing, again,,is the cel. 
This next procedure will indeed destroy the 
sketch. 
You take the cel and lay it on a completely 
clean and flat service. A surface that can take 
water. Take a clean sponge and semi-soak it 
in water. Begin to slowly sponge the back of 
the cel soaking the paper , but not overly 
soaking it so much that you will also desolve 
the paint..just the paper. After the paper is nice 
and soaked, begin to peel away from areas of 
least resistance (if there is such a place) and 
work you way around the really stuck on areas. 
Once you get the easy parts off make sure not 
to tug on the difficult parts too strongly or you 
will defintely have some paint loss. In any 
case, you may lose some paint. Try to control 
yourself the best way possible. Also, make 
sure that the area paper is has been soaked 
for awhile. Try to use your judgement and take 
your time. Let the cel dry on the back, before 
you try to do anything. Do not take a towel and 
try to dry off any water spots on the backside of 
the cel. The front side is okay, but be careful!

 Since the cels were not that valuable to begin 
with, this method might be okay for you. If you 
have an expensive cel, there are professional 
services in the USA that will do that service for 
you, but at a cost, but there techniques may be 
better than these home remedies. You can 
find those places in the archives here if you do 
a search.

good-luck

E