First of all welcome to the forum, @exhumedthallid . Just like with the recent thread of the Prototype Blastoise, I doubt anyone can give any definitive answers tbh.
But, I do want to thank you for your research and entire post. I actually have one of these cards myself (an Italian Base Set Pikachu). When I bought it the seller also stated it was a test print, but unfortunately he barely had any information… Here are some relevant parts of the PMs he send me at the time:
When I received it I was also quite skeptical of it being a real card (and I still am tbh). Apart from it being glossy, the colors and bolder font on the entire card are quite different. And when doing the light test it let’s through a lot more light than a real card. I’m still not sure what to think of it tbh, although I’m happy someone has investigated these cards, and I hope more information could be dig up. I personally deemed this card as a scam after I bought it, although since it being a test print was still somewhat plausible, it’s still in my collection.
Anyway, here some pictures of the glossy Italian 1st edition Pikachu I have (on the right), next to a regular non-Glossy version (on the left). I’ve also included some pictures taken through my 45x mini microscope to see the Rosetta pattern, as well as the light test (again glossy on the right and regular on the left).
Note that this last picture was taken at the same position and with the same light. My camera makes the glossy one darker because it detects a lot more light shining through the card… Not sure how to disable that on my camera so it would be a better comparison, but you can see the ‘Pokémon’ and Pokéball of the back are a lot more clearer on the Glossy print than the regular non-glossy version with the same flashlight, angle, and distance of the flashlight to the card.
PS: I hate Autumn/Winter… Too dang dark to take proper pictures with my crappy camera… 
The Potion stating ©1999-2000 is correct, since it’s an Italian card. Italian, Dutch, Chinese, and Korean Base Set cards will always have the ©1999-2000 copyright date, and German, French, and Portuguese will always have ©1999 (English and Spanish are available with both ©1999 and ©1999-2000). Some more information in this post I’ve made, to explain how to differentiate the foreign Energy cards for the Base Set based on the Energy translation and copyright date.
Greetz,
Quuador