The addition of the "San Luis &" to the diesels was to make the UP happy. A sort of "read the fine print" deal.
The passenger program has always been the "Rio grande Scenic Railroad". I imagine there are seperate books kept for it for accounting and legal proposes, but is part of the Iowa Pacific Holdings corporation. Also I think all the onboard personell that work on the passenger trains (not the operating employees) work for the RGS not SLRG.
This year it was decided to letter 18 for the RGS to get some market visibility.