I looked through my copy and you're right, it says 78 rows worked. But the photos clearly match up with only going through the chart once, which is 39. I also looked on Ravelry and not one person made a comment about it. My guess is that you and I are looking at older editions with an error. You can ask Alice Starmore about it by e-mailing her at email@example.com
. In the meantime, I would just carry on as you have been and not worry about the 78.