The disc number refers to the number of cases.
9-Disc: Prequels, OT, and 2004 SE (Which will be replaced as newer SEs come out)
12-Disc: Prequels, OT, 97 SE, 2004 SE
10-Disc: Prequels, OT, SE (I would have each movie in a two-disc case with the 97 SE on one side and the 2004 SE on the other), and the four Rowman discs (stashed in a 4-disc case)
Anyhow, here's a concept I whipped up for the spines that I REALLY am fond of:
