Well, they confused us all, because season 1 of Gunsmoke was a single set. 39 episodes on 6 discs. So starting out like that, everyone automatically figured it would continue on that way. Then with season 2 onward, we got the exact split you mentioned. Edit... and to drag it back somewhere near the topic, I keep waffling on buying Gunsmoke seasons 13-17. 17 seems to be quite popular, since it's out of stock at the big river.