I've got an Air China flight coming up in June, with 777-300ER aircraft on two of the four legs. Every seat map I can find online (including on Air China's website) show a 3-3-3 config in economy, spanning rows 31-60. But when going through seat-selection, the map shows a 3-4-3 config from rows 31-67.

is Air China going through a refit of this fleet? Does anyone know what differences to expect in the product?