LOL! I get the metaphor [not so obscure to me].

Firstly, there are two 'types' of hacked/modified cityXplorer maps available in Post #1, the full CX [Standalone, so needs no separate CN loaded] and the small CX [no CN content] which must be used with a CN of the same version. Then there is yet another 'type', the official CX sold by Garmin which are available as individual maps for just one city. They are available in the [Only registered and activated users can see links. ] also, but some haven't had the MMR components changed to FID 800, and because that original FID remains they are useless for Enhanced Pedestrian use in 37x0 and later devices [2011>]. Some of the original type such as Amsterdam have both versions, with FID 2419 unchanged for MMR, and the modded one with MMR FID 800.

Starting to get it?

Now, look at the GMapTool log in Post #4 for all the NA cities [Full/Standalone]. The individual cities have been combined into one big map, the NT [normal CN map] components have been unlocked and the MMR [EPM components] have had their FID changed to 800 so that with an appropriate unlock file they will work in all units supporting EPM including 37x0> devices.

Look at the second GMapTool log in Post #8. It shows the Small version which has no CN NT parts so must be teamed with the same version of the NA CityNavigator map to work, and again the MMR parts have had their FID changed to 800.

Finally, look at the 1st log in Post #8, it shows an official untouched version of London, all FIDs including the MMR are still 2969.

So, everything starts of course with the original single city official CXs.
Code:
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Now, in summary if you've now got you head around things: Think of the standalone CXs as having 2 main 'bits': (i) CN NT which can be unlocked by an unlocker and (ii) MMR EPM which can only be unlocked for a particular device by a valid unlock code in a *.unl file whether that's the original FID or 800.