That is definitely a Toei reproduction cel. I have one just like it in my collection (although, I do not have it up in my gallery yet). My cel has the same shading and line flaws as this one.
All Toei reproduction cels originally came sealed in bag with two Toei stickers - one on the back that seals the bag closed and a smaller silver one on the front. It would have also come with a separate piece of cardboard that has a handwritten number on it to indicate its number in the series. For instance, the piece of cardboard that came with mine says it is #19/100.
Toei made several Sailor Moon reproductions. My guess is that there are around 15 different ones because IIRC, there is one each of the 5 inner senshi from 3 different repro series. One repro series matches cels from each of their henshin sequences, one series matches cels from the second opening from the original season and the final series of repros are portrait shots that I have never been able to match up to anything.
All of these cels have registration holes but do not have any sort of number written on them. That makes it very easy for someone to come along and add a number later on and try to claim it as the real deal. I've seen this happen a few times over the years and I even got fooled and bought one of Sailor Mars way back when I first started collecting. Luckily this person didn't get ripped off too badly because $80 or less is usually what these repros generally sell for.
The funny thing is whoever wrote the bogus cel number on the cel was very close to the correct number. I have a real production Venus henshin cel that is very close to the frame that this repro cel was modeled after:
http://www.luna-art.com/cels/sm0697venus.htm
The cel number on my cel is A139 and I believe the repro cel comes 3 frames after mine and should be A142, so they were only 1 cel number off.
