There's a couple of ways to get rid of price tag 
residue.  If you can peel off the price tag in 
one piece, you can use it to remove the 
adhesive.  Kinda hard to explain (it's really 
easy to show in person) but use the tag to remove 
the adhesive.  Put the tag over the adhesive area 
and pull up on it.  The tag will take the 
remaining adhesive with it.  This also works with 
Scotch tape.  You can also use 90% rubbing 
alcohol to remove the tape, do not use nail 
polish remover as it will eat away the acetate if 
you use too much.

Ventilating cels really has no effect on the 
trace lines.  Trace lines are under all the paint 
in the cel.  The two things that make them fade 
are direct exposure to UV light, and the natural 
chemical decomposition of the paint.  Gas buildup 
is only applicable to nitrate cels, which haven't 
been used since the 50's.  Nitrate cels caused a 
lot of problems; the medium was unstable and they 
rotted easily.  In the late 40's acetate was 
introduced and quickly adopted by the industry as 
the standard.

The best way to protect your cels is to either 
frame them, or keep them in books and out of 
sunlight.  I've got cels that are 30-40 years 
old, stored in what would be 
considered "ventilated" bags and there's no 
fading on them.  Like someone mentioned prior, 
some studios cels are more prone to fading than 
others.  

Actually trying to store your cels in more of a 
vacuum like state is more detrimental to your 
cels.  Cels require a certain amount of humidity 
to stay in optimum condition.  To little humidity 
and the paint and acetate dries out.  Your cels 
get brittle and crack.  

Cheers,
Brian