If it's in a real NGC slab, then it's real. How do you know it's a real NGC slab? It would be very easy to make a fake slab. There are thousands of everyday people who are experts in making plastic molds.
There is a photo of NGC and PCGS slabbed coins by serial number on their Web sites. A comparison could be made with the photo.
The Chinese are less likely to counterfeit their own legal tender coins as it makes them subject to the death penalty. On the other hand, if you are concerned about this, having it in a slab, makes it more difficult to determine if it is all gold or not. Older bullion Pandas tend not to grade at 70 grade as the coins from that time had inconsistent quality controls.
I know where the Panda is from, I made the first reply to this thread, I don't think anyone is worried about the coin in the first post of this thread.
Maybe I'm confused. I thought you were asking for a story of something that is demonstrably a fake coin in what looks like a real NGC slab (whether it's real or not). ie; Fake coins in a NGC slab. And those are definitely out there: http://www.flickr.com/photos/coinforgeryebay/5860716598/ http://www.flickr.com/photos/coinforgeryebay/5860152185/ http://www.flickr.com/photos/coinforgeryebay/5518570411/ Here's a doctored NGC slab (presumably a real one with an inferior or totally fake coin inside): http://www.flickr.com/photos/coinforgeryebay/7123476591/in/photostream