UA-NYC kind of answered the questions asked of me, but:

I booked an international flight for May where all legs were upgraded and reflect an R code. The upgrades included domestic legs going from economy to first on a two-cabin plane. The international flights were upgrades from economy to business on three-cabin aircraft.

I was just upgraded (UDU or whatever they call it now) for a Saturday domestic flight from economy to first and the fare code changed to R.