How do you tell exactly which Japanese Pokémon card you are looking at?
Summary
Read the marks printed on the card. The expansion mark tells you which product the card came from, and the collection number tells you its place in that product; with both in hand, you will not mix it up with another card of the same Pokémon. A name search returns cards from many eras and rarities because popular Pokémon appear in so many products.
The four marks on a Japanese card
The official Pokémon Card Game site points to four marks. The expansion mark identifies which product the card belongs to. The collection number shows the total number of cards in that product and where this card falls in the count. The rarity mark shows how scarce the card is and appears on cards from expansion packs. The regulation mark is used at official events to define which cards are allowed.
For buying and price records, the expansion mark and collection number are enough to show you mean one specific card. Identical artwork with a different rarity mark is a different card.
Checking against the official database
Japanese cards can be looked up in the card search on the official site run by The Pokémon Company. It takes keywords and can filter by the three event formats, Standard, Extra, and Hall of Fame (殿堂). Each product page on the official site also has a "card list" button that leads into the same search.
Sources
- Pokémon Card Game official site, how to play (card types and how to read them, Japanese)
- Pokémon Card Game official card search (Japanese)
Details are as published on these pages on the date above and can change. Check the official page before you buy or submit.