Kloevis

I recently purchased a copy of Millipede that was sold as "brand new/unopened". I just wanted the cart- that it was even in a box was a bonus. Anyhow. I did open it and was looking at the cart- there's a stamp in the middle of the label (see pic- "264"). I haven't seen this on any of my other carts, and was curious about it. A quick googling did not yield any results pointing to "why". Anyone seen this before and know what it means?

Been looking for the XEGS Summer Games cartridge to complete the collection for years, now and giving up hope