Just because you purchase things from reputable dealers doesn't mean they are 
real.  Sometimes the source where the dealer's purchase from is a bit shaky. Doing 
your own homework is always good.  Blindly trusting people is not good!!!  Sure 
there are some dealers who have been doing this for years and may know their stuff, 
but there are a lot of them who do not even bother to check.  Their attitude is *Well it 
looks real, I paid a high price for it, it must be real!!*.
Also, don't be silly.. People will not fake cels with Belldandy's elbow only showing.  
The fake cels are the really nice ones!  Too good to be true ones!

I don't know in the case of these cels, but AIC had done a lot of repro cels.  Like back 
in the day they came to an American convention and had boxes of AMG repro cels. 
(and I believe, Tenchi Muyo, I cannot remember). They didn't bother telling people the 
were repro cels until you asked.  (or maybe people were so excited they didn't pay 
attention!!) So, many people bought for resale ($20-$100) and sold them at high 
AMG prices.. Some dealers aware of the fact they were repro cels and some dealers 
not aware of this fact.  Many of these repro cels are floating around, in people's 
galleries, people's collections and they do not even know it.  No one knows it unless 
you take the DVD image, blow it up and look for the same pinholes, missing paint, 
dust specs, etc.

So...  bottom line is, don't rely on anyone but yourself to do homework for cels. 

This repro thing was done only for the OVA.  I doubt they are doing it for the movie.  
However, that doesn't rule out the fact that someone in Japan could made copies 
from the genga.