All 242 cards are listed, and none of them is reconstructed from a list of names. The numbers, names and rarities come from the published card lists; the counts match the printed sets exactly — 55 / 53 / 54 / 80.
This is the first year in the almanac where the Japanese card list had to be found outside the usual database. TCGdex keeps a record for the Japanese ADV sets but it holds only a card count: the card array is empty and single-card lookups return nothing. Pokellector's Japanese catalogue stops at the 2002 set The Town on No Map. Bulbapedia has no separate page for these four sets at all — it files them under the English names. The lists here come from a card database that holds the Japanese printings and their scans.
HP, type, stage, retreat cost, attacks and illustrator are read off the English twin of each card, because the Japanese records do not carry them. Matching is by exact name first; where the English set prints the same Pokémon twice — which it does often, once as a rare and once as a holofoil — the two card faces are compared by perceptual hash and the closer one wins. Do not read this page's card list as a translation of an English set: EX Ruby & Sapphire has 109 cards against these 55, because the English edition folded in the half decks, and it carries eight Pokémon-ex where Japan's booster carried five.
Japanese names appear for Pokémon only. Every Pokémon name here is the official Japanese species name, taken from the species table — extended this year to Generation III, 252 to 386, because 2003 is the first year the almanac needs it. Trainer and Energy cards carry no Japanese name, and neither do the Team Magma and Team Aqua cards: their Japanese titles are マグマ団の… and アクア団の… and there is no Japanese card face in our sources to check the exact wording against. A missing line is better than an invented one.
Pokémon-ex are counted as holofoils and labelled separately. They are holofoil cards with a holofoil border, so they belong in the holo total — but they are a different thing to own, and the page marks them HOLO RARE ex rather than folding them into the ordinary rares. Seventy-eight of the 242 cards are holofoil on that counting.
What is still missing. The pack itself: wrapper artwork, the price of a pack in 2003, how many cards were in one, and the release conditions for each set. That is a standing task across every year of this almanac and it is not done for 2003 — so this page shows no packaging and quotes no price rather than guessing at one.
Some cards have no face. Seventy-two of the English cards on the English page — the separately numbered holofoils H01 to H32 of Aquapolis and Skyridge, and the eight same-number pairs 50a/50b, 74a/74b, 95a/95b and so on — have no card image in the source database at all. They are listed with their numbers, names and rarities, and no picture is substituted. A missing face is better than a wrong one.