It’s clear that many of these cards had multiple distributions of the same card, a lot of which are documented on Bulbapedia but not always with clear indication of whether the different releases are different. Many cards which were distributed through more than one event appear identical, but I am sure there are some who are different.
As an example of what I mean, CoroCoro distributed a set of Farfetch’d, Jynx, and Cubone at one point in 1998. Later that year, a mail in contest had a prize of the same cards along with Surfing Pikachu and Flying Pikachu. Since these releases were both from CoroCoro and both distributed in the same year, it stands to reason they are probably the exact same cards with no variations. But unless you owned both or already knew from experience, you could only assume one way or another and you might be wrong.
If there is already a thread with this list that I missed, do please link me to it. Otherwise, do you know of any Japanese promos (1996-2002) whose multiple distributions produced variants between them? Bulbapedia is really clear on who is glossy and who isn’t so I’m looking for more obscure variants it might be important to know about.
Edit (from below):
Pokémon Card Trainers Vol. 4 insert (December 1, 1999) came with a Murkrow promo and a Darkness Energy card, which is listed as a promo on Bulbapedia. But is this card actually unique in any way compared to the regular Neo Genesis Darkness Energy?
The corocoro shiny mew has multiple foil variants, a thread on that has also been made: www.elitefourum.com/t/shiny-mew-cards-how-many-are-there/21737/1
This is really hard to know from photos though since this card normally has multiple foil layers, but there are multiple versions of this one.
That Shining Mew set I have seen mentioned here in that the only place either of the variants have been seen are in that photo - is that true? Is it even realistic to try to locate them?
The Pikachu thread was helpful, helped me confirm which releases were which on my spreadsheet. Thank you.
Apart from the threads already mentioned by @thymeee , these two threads are useful as well:
www.elitefourum.com/t/mewtwo-wb-gold-stamp-movie-promo-japanese-ver/22725/1 Just like the the English Shadowless Base Set yellow cheeks Pikachu has two different prints, one in the US Shadowless Base Set and one in the Japanese Pokémon Song Best Collection CD (the one printed in Japan has thinner cardstock), a similar difference can be found for the English WB Mewtwo promo, which has a Japanese release that was included in the VHS.
www.elitefourum.com/t/super-energy-retrieval-non-glossy-japanese-promo/19503/1 Super Energy Retrieval has four versions: two glossy (Fan Club promo and Pokémon Best Song Collection CD promo); one non-glossy (unknown origin); and one from the Neo Genesis set. Later in that same threadKEI also mentions how to distinguish the four glossy cards (Mewtwo, Mew, Super Energy Retrieval, and Computer Error) from the Pokémon Song Best Collection CD promos with their earlier releases by looking at the cross-section of the card with a loop.
I just took a pretty big risk on that English Kanzenban VHS Mewtwo from a vague Yahoo Japan listing. This card is pretty much impossible to tell apart in pictures alone so I hope it ends up the right one… 50/50. It hasn’t come in yet so I don’t know.
KEI’s documentation has been incredible, honestly. Some of the only record of this stuff on the entire internet at this level of detail.
Pokémon Card Trainers Vol. 4 insert (December 1, 1999) came with a Murkrow promo and a Darkness Energy card, which is listed as a promo on Bulbapedia. But is this card actually unique in any way compared to the regular Neo Genesis Darkness Energy?
There might be other ways to tell them apart, but the most obvious from my experience is that the Trainer Mag promo lacks a rarity symbol in the bottom right - it’s hard to tell depending on angles as the card itself is black, but the Neo Genesis version has the usual black star rarity symbol to the right of the set symbol.
Edit - it also has the release text on the bottom gold border, you can read the ‘Vol. 4’ part in English.
It hasn’t come in yet so I don’t know.