I said this before in some other topic but I don't think a lot of people even saw it. Well anyways when the Sand nin are in the OP, they participate in the canon story. They've never been in any filler episode so that doesn't make sense. I double-checked and every episode they're in, they were also included in the OP (and vise-versa). This might be a sign of Part 2 or ending fillers, but that seems hopeless. I just thought I'd point this out.