I have a trip to SAN this Wed and mine is showing "First Class R", but I used miles to UG when I purchased the ticket, The wife who is flying on miles is "First Class A".

I do know that if you upgrade when you book the flight it does come out of the "R" bucket. If there is no "R" availability at that time you book you can't UG the flight in advance... Now EUA is a different story. For me at least it works fine, including the platinum companion EUA benefit.