If you’re asking whether reproduction cels 
masquerading as production cels are a big problem 
in this hobby, I think the answer is no, with a 
few exceptions.  The most notable exception is 
Ah! My Goddess OVA (not movie) cels, particularly 
of Belldandy.  AIC made a bunch of repros; the 
ones I’ve seen are relatively close-up shots 
(waist-up or head shots).  There doesn’t appear 
to be a record of which cels had repros made from 
them, nor how many, and a bunch of them made 
their way to the US and often onto ebay.  It’s 
probably a good idea to check any decent AMG OVA 
cel you’re thinking about buying (which should 
become easier with the release of the DVDs).  

The black xerographic lines are the same in the 
production cels and the repros, so you have to 
look at hand-drawn lines and painted areas to 
look for differences from the screen shot.  As 
stated in the previous post, there is often (but 
not always) an area where the color in the repro 
is different from that in the screen shot.  
Perhaps AIC asked the artists to do that on 
purpose on many of the repros.   

As for other series, I believe someone on the 
forum has an example of a Tenchi repro on his 
site, and I have an El Hazard cel that has an AIC 
stamp but wasn’t used in the video.  However, 
these are probably unusual in the world of cels.