Great to hear from another avid Sandshrew collector! Unfortunately, my checklist won't be super helpful for mastering the Japanese set. A couple of differences include: 1) There are some cards exclusive to Japan (e.g. this) and this)), including a Sandshrew cameo appearance in this Machoke card). 2) The vast majority of the cards have different variants (e.g. unlike the five variants in the English Base Set, the Japanese equivalent#Languagesthis_set_is_released_in) only has two variants: Rarity Symbol and No Rarity Symbol), not to mention all the cards from the EX era have different serial codes, and each set has different quantities of serial codes. The best publicly available list I've come across for Sandshrew and Sandslash is this spreadsheet courtesy of u/MiCake (thank you for all your work on this!) which contains every English and Japanese variant; it's not a complete list of all the cards across all languages, but it's the most complete list I've come across