Originally Posted by
CPH-Flyer
It sounds like a reasonable explantion, they do have to flag the inventory for paid upgrades somehow. I seem to remember that UA also used R to show space available for upgrades with GPUs, but as I never were a big United flyer and have only ever used friends' GPUs I am not the most reliable source on that.
I was going to say no regarding UA, but did a quick search. R is their new discount bucket for Premium Plus (their new premium economy product) and they have upgrades in RN for this. If you are talking about pre-CO merger then I suddenly have a vague recollection that they used R. But UA is not part of the Amadeus family either.
If my theory is correct, then it is surprising since SAS would normally not make this available in the public domain.