No worries! It does sound likely, it was definitely from a time where people had to do everything they could to fit games onto the cartridges!

The Wikipedia page [1] claims* they had an MMU on the expansion cart - so they could have taken your advice :)

* I couldn't find a source, and AFAICT the DeSmuME emulator [2] seems to treat it like a big chunk of linear memory?

[1] https://en.wikipedia.org/wiki/Nintendo_DS_Browser#Memory_Exp... [2] https://github.com/TASEmulators/desmume/blob/master/desmume/...

E: I forgot about the mobile Opera ports, that also tracks - I'd love to read about the engineering that went into them!