I check my english ones and they all match the pattern. I however also checked some Dutch 1st eds base set just for fun and those are (non holo’s) also -15, same goes for Dutch unlimited fossil.
Not sure if it even matters or is useful in any way!
Maybe check english jungle/fossil, if those are all -15, maybe these are printed late instead of first?
And yes all non holo shadowless should be +15 from my findings.
First print for non-holo is prob gonna be the 1st ed stamp for now. Havent completely gotten there yet lol. These patterns change and vary over the yearsive got a good understanding but this thread cant fit it all lmao. U interested in the discord?
99% of holos after thick stamps are +15
All the belgium made stuff is -15 to my knowledge. Should have the “e” shade error too. 1st ed dutch are also 99-00 print
Great! Well done for finding this stuff!!
I’m not a discord user, but it’d be amazing if you could keep those of us on the forum up to speed as you keep discovering more. 
Will do the best i can. Hopefully i can track down some uncut sheets and continue the research
If anyone ever cracks some packs, we can go further… @packyman 
That’s indeed been what most people think, that they forgot to edit it out when going from 1st edition to Shadowless. Especially considering it was just the Pikachu that was effected, despite that all cards of the same theme deck should have been on the same sheet (except for the holo Mewtwo of course) - or the cards of the ZAP! and Overgrowth theme decks at once to be more precise. 
Ah, the wonders of the early WotC print runs/releases. I sometimes do still wonder what the actual order of prints were, considering that the actual release order were somewhat jumbled up.
E.g., the first ‘released’ English Base Set cards weren’t even 1st edition, they were Shadowless: December 1998 demo pack (here an opening video). Then we had the Trainer Decks A & B, which are ©1999 unlimited edition cards, but with red-bordered backs. And only then the 1st edition Base Set released on January 9th, 1999.
Speaking of Trainer Decks A and B, I got curious. My Trainer Deck A Fighting Energy is +/+ (+15 front & +15 back), and my Trainer Deck B Water Energy has a +15 back & front I dunno (there is a severe lack of Magenta on Water Energy cards - if there is a specific area on the card I should/could check, let me know..).
Iirc, that alignes with the +/+ you’ve found on (the majority of) ©1999 unlimited edition cards, right?
Greetz,
Quuador
I would assume trainer decks were released after shadowless based off the +/+ patterns. It you couldnt see magenta, look for cyan. If cyan is -, magenta is +
Then the Trainer Deck B Water Energy front is +15 as well, as expected. And apparently it did have some Magenta dots, but they were very tiny and almost not noticeable, even with my 40x loop.
Greetz,
Quuador
Had a quick look at three thick stamp holos I have to hand and they’re all -15 magenta - really interesting discovery!
Seems the disco holos are +15 too.
Most of the scans on Fanatics Collect are high enough resolution to see the dot alignment. I looked at over 20 scans of thin and thick stamp holos. They all correspond with your findings.
Got pics of the disco stuff?
Thats some pretty solid evidence🔥
Only screen grabs of the Fanatics Collect scans I looked at. Like the back of this Venusaur Disco.
The screengrabs reduce the quality, so better to look on the website itself.
Definitely makes me wonder why these test prints were printed if they had already issued the first run of of foils. Havent done my hw on them yet but id like to put my eyes on them at some point and actually see them
The first few sets were Galaxy foils before they switched to Cosmos foils. Maybe these Disco foils were test prints as alternatives for the second Cosmos foils. 
Also, now that we’re talking about test prints anyway: the Protostoise cards with smooth foil appear to have +15 fronts and the later Galaxy foil copy -15 (I think). 
The backs aren’t too important, since they’re MTG backs, which are (a.f.a.i.k.) always -15, since the magenta dots in some of the orbs on the back are used to determine if cards are real (e.g., the L-shape in the green dot).
Here some close-up pictures, to judge for yourself. The pictures in this first quote are taken from Travis’ video of a smooth foil copy:
And this quote is from the Galaxy foil copy, from CGC’s article:
And here also the back for two of the (smooth holo) copies from CGC’s article.
As for the holofoil of those Protostoise, they’re either smooth or Galaxy:
Greetz,
Quuador
I check my cards and these were the results:
-1st ed Thick holo: -15
-Shadowless holo: +15
-Disco holo (shadowless layout): +15
-Unlimited holo: +15
In theory then thick stamps may be a different print run than thin and shadowless as both seem to be +15? Or it was all the same print run and then used a different printed back when they released thick stamps to the public, and another for thin and regular shadowless. Curious to see if there are -15 shadowless cards out there.
For the love of science I checked my +100 shadowless Gyarados and they are all +15, and I’m aware Gyarados was released both in Base Set and theme deck. But that depends on how they printed the shadowless run. Would be interesting to see the 1998 demo boosters.
thank you for your service
