[Geocoding] Does Nominatim need all OSM data to be efficient ?

[Charles DESNEUF]

Hi all !
I tried to install my own Nominatim server and I have some issues with the
responses it returns. I need to run a reverse geocoding service which is
able to return information such as country code, state/region and
locality(city, town,...) but nothing more specific.
I have created a new osm file using osmosis, from last-week planet file,
with a the tag-filter option to get only elements(nodes and ways) with tags
boundary, border_type and place and imported it using Nominatim setup
script.
While I was running some tests, I noticed some errors in Nominatim
response(Moscou with US country code, bad state in Rennes, France(Pays de
la Loire instead of Bretagne, ...).
Of course, the Nominatim instance running on Poldi returns valid
information.
Does Nominatim need all OSM data (streets, ...) to be efficient or did I
miss something (a tag ?) ?

Thank you in advance for your help.

Charles
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