Yes, that's why I mentioned a possible issue with "discarding" in my post.I remember that this topic has been discussed before, There have been guesses about tax, customs, trade or environmental reasons for the marking. I think is that this guess by @mikling is right and it is caused by stricter environmental regulations in the EU than in other parts of the world. So the cartridges are identical except for the labeling and are region independent.
I guess these rules were introduced sometime between the introduction of the CLI-521 and CLI-526 cartridges. See this and notice the waste symbol and the Canon Europe N.V. marking on the CLI-526 cartridge, click to enlarge:
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