It seems the Shiny Zoroark was indeed lost, so got refunded and bought another one. As for the Shiny Vaporeon, I have no idea where it’s going… I got a tracking number (after I opened a file that it hadn’t arrived yet) which stated it was on its way to India, and when customer service of CardMarket contacted me they stated it was in Madrid Spain… So yeah, I’ll wait a bit to see if it gets back to the seller and they can reship it to me, or whether I should just ask a refund and buy it elsewhere again.
So, I’m gonna bump this one last time. Let me start by stating some additional artwork differences I’ve been able to come across myself that weren’t mentioned yet in this thread (minor spoiler for my upcoming article when I have all cards in hand 
):
- The yellow stripes of Ekans from Team Rocket go around the body, where only the belly is yellow for all other Ekans artworks
- The Poliwag from Base Set has a light blue mouth instead of beige like the other artworks
- There are light grey Machop, Machoke, and Machamp; blueish Machop, Machoke, and Machamp; and greenish Machop, Machoke, and Machamp. But Machop and Machoke are both supposed to be grey, and Machamp is supposed to be blueish.
- 1/3th of the Magnemites have the red part of their magnets at the top-left/bottom-right; 2/3th of the Magnemites have the red part of their magnets at the top-right/bottom-left. The Magnemite from Triumphant has both red parts at the bottom (although it’s mostly due to the artwork angle).
- The red/blue parts of the magnets for the individual Magnemites of Magneton are at the same sides for almost all artworks (as it’s supposed to be), but they are criss-cross from each other on the Magneton from Fossil, Lt. Surge’s Magneton from Gym Heroes and on Jasmine’s Magneton from the VS set (and one of the individual Magnemites of these Magnetons is also upside down).
- Erika’s Exeggcute from Gym Heroes has five eggs instead of six
- Wooper from Secret Wonders has very light purple stripes, where all the other artworks are very dark purple
- Mantine from Neo Genesis has another miniature fish, instead of a miniature Remoraid like the other artworks
- The first few Stantler cards had beige tails, and all the later artworks have brown tails
- The first few Mightyena cards had black noses, and all the later artworks have red noses
- Nincada from EX Dragon has beige forelegs, where all the others have either light brown or dark brown forelegs
- Some Normal Forme Deoxys have two regular arms (like the one from POP 4); some Normale Form Deoxys have two tentacle arms (like the one from the 10th Movie Commemoration Set); and some Normal Forme Deoxys have one tentacle and one regular arm (like the one from Legends Awakened)
- Roserade from Ultra Prism has a purple instead of blue flower, and Roserade from Stormfront also has a purple instead of blue flower, and in addition two leaves as cape instead of three
- The small berry of Cherubi from Unleashed is at the left side instead of the right side like the other artworks
- Gabite from Dargon Exalted has blue claws instead of grey like the other artworks
- Kid’s Weavile from the Movie VS pack has a dark orange crystal; some Weaviles (like the one from Diamond & Pearl) has a light orange crystal, but it’s supposed to have a yellow crystal (like the one from Secret Wonders)
- Chandelure from Noble Victories and from Phantom Forces both have dark purple flames, where all the other artworks have light purple flames (like the one from Plasma Freeze)
To quote something @woolsluk once said to me when I mentioned my wanted list for Pikachus soon after I joined the forum:
And I indeed am with this collection as well. 
If anyone knows of any more minor differences between artworks for the Pokémon TCG, no matter how trivial as you can see from the list above, let me know.
Greetz,
Quuador