The cards themselves have no difference. Only the inserts are different. But you’re indeed correct there are (at least?) three different insert versions for the WB promos. Here all three Pikachu cards from my personal collection:
Usually these inserts differ per region they were released in. If I’m not mistaken, the square-cut Catch Mew and Collect Four versions are from the US and the Pokémon League version is from the UK. I’m not sure if and which version was released in Australia for the WB promos.
Here six from the US, UK, second US, Germany, France, and Italy:
And here the very rare variant with Game Boy Color insert from Australia, which I was finally able to buy after searching for it for 2.5 years a few months back:
The promos inside these sealed backs are all the same though for the WB promos. (And for the Moltres the English ones have a misprinted and corrected illustrator version; and the German, French, and Italian sealed packs of course contain the Moltres in those respective languages.)
Very nice question! @quuador, could you make a complete “guide” for these kinds of “inserts”? I was watching this video and saw all these different typs… and felt a little overwhelmed
Sorry, apart from what I mentioned above I’m not too familiar with every insert of every promo, especially the non-English ones. I only collect the Moltres in all sealed variations, and the three English Pikachus I have I just bought on impulse as a triplet last year. No doubt I could figure out most inserts by gathering a lot of information from videos like the one you’ve linked of TCA Gaming and pictures on eBay listings, but it’s not really in my own interest tbh.
If you have questions about an insert in general you can always ask me. But sorry, I’m not going to write an article about these.