Some countries do not have fpa files (as all did not have some time ago) but iGO introduced fpa system which is more complex then old (house numbers in fdl) and some providers use fpa for some coutries.
So if those address points info are moved in fpa (for specific country and specific map provider), then you must have fpa to be able to see house numbers and to be able to set exact house number as destination.
In some situations you may be able to see house numbers on map, but you will not be able to set that exact address as destination without fpa, which is more important than what's on display.
I have that situation in Croatia with TomTom maps is some places.
In new release fpa for Croatia is present, but anyway not all house numbers are available, but if fpa is removed I can not use house numbers for destination.
I hope this is more complete answer.