Sorry in advance to go complete off-topic for a moment, but:
Things like that Ponyta is what makes it so hard to find certain information, since Pokémon releases can be very inconsistent… 
To give a few other examples of inconsistent releases:
- The Japanese Pryce’s Lapras is a similar example as the Ponyta. The Pokémon VS set was only released as 1st edition, but this Lapras is available as unlimited edition in the Pokémon Card Information vol. 3 magazine (which was actually released a month before the Pokémon VS set came out). (I wonder if the unlimited L1 starters have a similar loose release?)
- The English Secret Wonders Reverse Holo versions for the Breloom, Flaaffy, Quagsire, Bulbasaur, Carvanha, charmander, Shellos east sea, Shellow west sea, and Squirtle cannot be pulled from packs in the actual set, but were released separately as blister promos.
And when we add all languages into the mix, things can become really confusing sometimes:
- The WotC #4 Pikachu promo was released in Dutch, but the other WB promos #2 Electabuzz, #3 Mewtwo, and #5 Dragonite were not. This one can be explained, although in general it’s still confusing. The reason why the Pikachu was released in Dutch and the other WB promos not most likely has to do with the Pikachu World Collection 2000, which contained a #4 WotC promo in Dutch with the stamp. So they probably also released it without stamp, since they were already printing it anyways. (A similar thing can be said about the other Pikachu World Collection 2000 languages, with the exception of the Chinese Jungle Pikachu, and a non-holo version of the English Birthday Pikachu promo.)
- The EX Legend Maker set is released in English, German, French, Italian, Portuguese, and Chinese. But the Portuguese and Chinese sets both lack the Secret Rare Pikachu.
- The Mysterious Treasures set was released in Spanish, but didn’t contain any Reverse Holos. There are quite a few Spanish sets that lacked Reverse Holos tbh, and the entire XY era also lacked Portuguese Reverse Holos. But, the Mysterious Treasures and Majestic Dawn Burger King Reverse Holos (with DIAMOND & PEARL and PLATINUM stamps respectively) were both available in Spanish, printed in Argentina (even though the Majestic Dawn set itself was never released in Spanish).
And I could probably name hundreds of similar examples. Just today I learned about a new one from Eric’s collection thread: the Spanish SH Secret Rares are Holofoil instead of Reverse Holo like the English, German, French, and Italian versions.
Ah well, it can be frustrating at times, but it also kinda makes it interesting to go after all variations in all languages of a certain Pokémon, especially a popular one like Pikachu. 
Anyway, sorry about going completely off-topic. Just thought I’d give a bit of background why finding information for certain releases in the Pokémon TCG can be so difficult to track down and get facts/evidence for, since there are so many possible ways a certain card could have been released as, somewhere in the (distant) past. And in a lot of those cases, there isn’t much to go on.
Greetz,
Quuador