@Purin,
If the distribution carts were loaded in-house (literally at the office with a dev kit), then it would make sense to have multiple identifiers, but not all will be unique. That is because they would have compiled the ROM on each computer using the dev kit, which makes a specific build identifier, and used that to load the carts. With 3-5 PCs, you can load 500+ carts in a few hours and you would have 3-5 separate identifiers.
Still not traceable though. Engineers are notoriously lazy too (personal experience here with myself too). They delete files they don't want anymore. They don't migrate files to new PCs cause they don't want to deal with legacy stuff. They throw projects onto tape drives and literally store them in a closet to rot. And they never keep track of their own code let alone project builds. And back in 2003 I doubt they used control systems for compiled ROMs. Code maybe (CVS), but not ROMs.
There is LOTS of evidence (especially in the code) that the distribution carts were the worst hack job in the world. They didn't even test them thoroughly. Literally some junior copy/pasted some code they found. redeemed a single pokemon and declared victory. Even in 2005/2006, a late mew distribution used jirachi code and mew code together, despite having the aura mew code available. Probably because the guy making the standard library (gcea/misturin/10 aniv/etc) was not the same guy who was asked to make the other mew. So the guy used legacy code he found somewhere from 2003, most likely the ruby debug commands (as we know mystry mew also uses old as shit generation).