Faust guide anomaly, or oversight?

[Caius]

I'm not sure if mods can do it now.

[Whacker]

Smooth move there Germanicus.

j/k mate

As far as I can tell your observation is correct. The unit must have the "free_upkeep" modifier (or whatever it is exactly) in the export_descr_units file. Further, in order to get the free upkeep, the village must be capable of building the unit, otherwise it won't get the cost deducted. Lastly, the number of slots for free upkeep depend on how the city/castle level is configured in the export_descr_buildings file. If the unit is being given free upkeep, it will show up as having a blueish background on the city's garrison view.