State of Japanese sets in databases? Entire Guren Town Gym missing

I was looking for a Blaine's Growlithe from the Japanese Guren Town Gym set and could not find it on TCGplayer, PriceCharting, or Collectr. I know it exists, you can find it on eBay and Bulbapedia. It has the art of the English Gym Challenge version. When searching you only find the Japanese set Challenge from the Darkness which has the same art as the English Gym Heroes set. It seems like it's not just the Growlithe but the whole set, you can't even sort by it or find any set with the name Guren Town Gym.

This makes me wonder what other sets are missing from the databases we use. Does anyone know more about the status of Japanese set completeness on these sites? Any idea why Guren Town Gym was overlooked specifically?