Great question! And unfortunately one I’d like to know the answer of myself.
Just some additional information for those who aren’t aware of it: all cards during the ex era (or ADV and PCG eras in Japanese) have codes at the bottom-left of the card. These codes always consist of 9 alphanumeric characters, grouped per three with hyphen separator (i.e. Y7B-F26-0FN). What the purpose of these codes are I have no idea, which is primarily what @gabrielgv 's question is about.
One important thing to note about these codes: non-Holo Commons, Uncommons, and Energy cards can have multiple codes in some of the sets. Promos; stamped cards; holofoil variations; deck cards; etc. all have just a single code. All Holofoil Rares; non-Holo Rares; and Reverse Holofoil cards have a single code as well. As for the others:
- Non-Holo Commons (English, German, French, Italian, Spanish, Portuguese): Non-Holo Commons will have three different codes for the mentioned languages, in the following sets: EX Ruby & Sapphire; EX Sandstorm; EX Hidden Legends; EX Team Rocket Returns; EX Deoxys; EX FireRed & LeafGreen; EX Emerald; EX Unseen Forces; and EX Delta Species.
- Non-Holo Commons (Japanese): Non-Holo Commons will have have four different codes for the following Japanese sets: ADV Expansion Pack; Miracle of the Desert; Rulers of the Heavens; Undone Seal; Flight of Legends; Clash of the Blue Sky; Rocket Gang Strikes Back; Golden Sky, Silvery Ocean; and Mirage Forest.
- Non-Holo Uncommons and Energies (English, German, French, Italian, Spanish, Portuguese) 1: Non-Holo Uncommons and Energy cards will have two different codes for any of the earlier mentioned languages, for the following sets: EX Ruby & Sapphire; EX Sandstorm; EX Hidden Legends; EX Team Rocket Returns; EX Deoxys; and EX FireRed & LeafGreen.
- Non-Holo Uncommons and Energies (German, French, Italian, Spanish, Portuguese) 2: For the EX Emerald set the non-Holo Uncommons will have just a single code in English, but two different codes in German, French, Italian, and Portuguese (no idea why that’s the case). I’m not sure if the same applies to EX Unseen Forces and EX Delta Species, for which the English non-Holo Uncommons also have just a single code, but I assume the other languages do have two different codes in those sets for non-Holo Uncommons as well.
- Non-Holo Uncommons and Energies (Japanese): Non-Holo Uncommons and Energy cards will have two different codes in Japanese for any of the earlier mentioned sets: ADV Expansion Pack; Miracle of the Desert; Rulers of the Heavens; Undone Seal; Flight of Legends; Clash of the Blue Sky; Rocket Gang Strikes Back; Golden Sky, Silvery Ocean; and Mirage Forest.
The Chinese EX Legend Maker set won’t have different codes, and for the Korean ADV Expansion Pack set I’m not sure.
The cards in the EX Team Aqua vs Team Magma and Magma VS Aqua: Two Ambitions sets all have just a single code. Not sure why this set was skipped regarding the Commons/Uncommons/Energies having multiple codes.
Here an example of all three non-Holo English EX FiredRed & LeafGreen Pikachu cards with different codes:
(open the image in a separated tab to actually see the codes)
As you can see, only the last three characters differ for the same cards. The first six characters are the same for all two/three/four same non-Holo Common/Uncommon/Energy cards.
A list of all English codes can be found in this Excel spreadsheet, which was compiled by @tonysandlin in this thread back in 2016.
Here also a related thread by him, where he tried to find a pattern for the codes in 2014.
That should probably clarify a bit what ex era codes we’re talking about here, and how there can be multiple codes for some cards. But even through these different codes have been discussed as early as 2012 here on the Efour forum, we still don’t know the purpose of the ex era codes in general unfortunately… 
Anyone has any idea what the purpose of these codes might be? Even if you don’t know the answer, feel free to just give theories of what you think the purpose of these codes might be as well.
Greetz,
Quuador