The Roc mold has been tweaked a number of times over the years. The least stable mold is the Ontario mold. Most stable is the Rancho Cucamonga mold and in between is the San Marino. You can tell them apart by the engraving on the under side of the disc. It refers to which factory the mold was created at.
The names are from the cities where they use to have their factory at. The rest is as "Star Shark" has said. You can still get all the molds when they make special runs. I mainly see them as CFR discs. Some people will tell you that they are not the same as the true molds and that the San Marino mold is the best out of the bunch. I prefer the Rancho Roc in Champ plastic, but that's just works for me.
I carry 2 Ranchos, 2 San Marinos, and 1 Ontario. They are all beat differently and I can do what I need to on 99% of my upshots and short tee shots with these 5 discs. For me, the Ranchos are the most stable and the straightest. The San Marino gives me a nice gentle turn over and the Ontario I can flip and turn hard if I need to. I love them all and with different wearing on each, they are all different discs.