[Talk-GB] highway_authority_ref vs official_ref

[Nathan Case]

Hi all,

I've been looking through some of the UK's "frequently used tags without 
a wiki page" 
(https://taginfo.openstreetmap.org.uk/reports/frequently_used_keys_without_wiki_page) 
with the aim of documenting some and the tag "highway_authority_ref=*" 
has popped up.

It's used almost exclusively in the UK (99.5%) and it looks like most 
values were part of some import in 2019 
(https://taginfo.openstreetmap.org/keys/highway_authority_ref#chronology). 
The values indicate that it is used on C and U class roads in the UK.

I was wondering if it is functionally the same as official_ref? This is 
documented (https://wiki.openstreetmap.org/wiki/Key:official_ref) as 
being for the "C-road network" and is used more globally, but does have 
significantly fewer uses overall (~17k vs ~42k).

Is there some history here, or just the classic two tags developed 
separately of each other? Do we have a preference for which to use - if 
they are indeed for the same thing?

This will help inform what I document on the wiki for this tag.

Thanks!