Another important thing people should notice is the setting.
Skypeia and Water 7 saga was a coherent part of the story, they were a creation when Oda was expanding the story. In another words, Skypeia and Water 7 saga is mostly filler-like the context of the larger story. So, Oda didn't plan them that tightly rather he was drawing/writing freely.
However, right now, the story is more tightly controlled and story bleeds over from one arc to the next. This means that Oda has to plan more thoroughly with less chance of wrong prediction.