Hi, welcome to OSM.

We do not tag refs for tertiary and unclassified roads as these are only used internally by local authorities and they are not signed.

Telling a normal user of OSM to follow the C2073 is only going to confuse as there are no signs.

Sabre's wiki is also not a valid source for OSM, we do not know what source they have use to obtain this information.

Where we do map such references we use the tag highway_authority_ref https://wiki.openstreetmap.org/wiki/Key:highway%20authority%20ref?uselang=en

Cheers Phil