CoroCoro Jumbos

Hi,

I have a very important question I need an answer to.

For Japanese CoroCoro Jumbo promos, you can hold them up to a light. For some of them, the light shines through, and for others, light does not shine through. It is acknowledged that this difference may be the key way to tell if a CoroCoro Jumbo is fake or legit.

So, can anyone please tell me a definitive way to distinguish a fake CoroCoro Jumbo from a legit one?