This is from 'Note on the Text' in NA:

'A more clear-cut case of restoring the author's intention occurs when we give the volume division. Austen, like other novelists, expected her work to appear in at least two, if not three, volumes, and usually seems to make provision for a break somewhere in the middle. Catherine's removal from Bath to Northanger gives the printer one obvious opportunity, but that is past halfway, and he has adopted instead the false climax at the end of I, xv, of Isabella's engagement to James Morland. Here there seems a good chance he followed Austen's plans.'