[OSM-newbies] New or existing relation?

[Bob Hawkins]

SomeoneElse,
Thanks for your helpful response.  I take on board you are not a JOSM user, 
and if that means you cannot answer this post, I hope another 'someone else' 
can!
I wish to add a relation to part of the Chiltern Way near Henley-on-Thames. 
'Chiltern Way' is listed under 'Table of other routes' in the page of the 
link you included. The 'Route relation' column provides its id 23309, and 
"b" and "a" in the 'Route relation' column provide the key and value 
information I need.  What I do not understand, however, is how my part of 
the route will be given the same id as that already in existence in another 
part of the country.  I have carried out a small test in the dialog that 
appears when I choose to create a new relation, by entering the same keys 
and values as for the existing Chiltern Way.  Clicking 'OK' in the dialog 
adds the new relation to the relations list, but with '[id: 0]'.  I am 
unwilling to upload the data until I know how and when the id is added, and 
whether it will be given the same id as for the existing Chiltern Way, based 
upon its name being the same, perhaps.