@axxtw
To take a short detour back to basics, because if you're confused as to the basics Neil's in-depth explanations will just continue to befuddle

Think of the City Explorer enhanced pedestrian data (the MMR data) as an overlay -- the bus routes aren't much use without an underlying street map to put them in context.

The CX (small) is just the overlays - the MMR data. It requires the matching street map (City Navigator) to be of any use (or even function).

The CX (full) is both the overlays and the underlying street map (taken from CN).

So in the CX (full) you're working with there is an NT section for Chicago -- that's the same piece of street map that City Navigator uses to show Chicago.
Then there's also an MMR section for Chicago -- that's the enhanced pedestrian mode data for Chicago, useless without the underlying (and matching) street map (NT section).

That's why Chicago is listed twice -- you have both the Chicago street map (NT) and the Chicago pedestrian data (MMR), and both are needed for the pedestrian data to be used.

Hopefully that will help put the unlocking requirements and the difference between CN, CX-small, and CX-full in a better context.