Yep, that's it.

It occurred to me that when Gurth's applies, it also applies to any morphs... it's just some are obviously easier to spot than others. For the particular case of being able to divide the grid into a 3x6, 3x3, 6x6, and 6x3 that are all rotational symmetric and all share the same digit pairings, it's not

too hard to see that the symmetry applies. (And I happened to have a 9.0 which reduces to singles with Gurth's, so...)

I'm wondering if there is some simple generic process for determining whether a puzzle is a potential candidate for morphing in this way. In such a puzzle, there must necessarily be a pairing between rows, columns, and boxes, but maybe that's not a sufficient condition.