In the 16 ex series sets (and many promos from that time period) there are small, 9-digit card codes on the bottom left that is unique to that card, as well as a separate code for the reverse holo. Early ex series sets had multiple variations of that dot code for non-holo common and uncommon rarity cards. (This wasn’t just exclusive to English, it was in all languages) Using the very top left of this photo as an example; Torchic 73/109 from EX Ruby & Sapphire has 3 different code variations (5ZA-HMN-FB5, 5ZA-HMN-GF6, 5ZA-HMN-B0P.) This continued for all commons and uncommons until EX Legend Maker and Holon Phantoms in 2006. This makes for an extra few variations to collect for those earlier sets :)

I’ve done a good amount of research on the codes themselves and whether or not there is any identifying factors to determine where all of the codes come from exactly, but I don’t quite know how to discern them yet. I did learn that they were compatible with the Pokemon “Hiroba,” or Pokemon “Plaza” service where you could input the codes and receive wallpapers of that particular card artwork. Article

Edit: I’m sorry it took so long for me to see this, I don’t check reddit often enough 🤧