Thanks for the information. 
I assume all of this is true of the City tag too?
For my application, I am updating address and contact information of licenced premises and importing them from OSM into my database. I use county as a search filter in my application, so that's why I fill it in. 

Do you know of a way to extract the county administrative boundary for a node? I don't see an easy way of doing it using the API.
