I find that bread recipes are more guideline than Gospel. I rarely
use the exact amount of flour a formula calls for. Different kitchens
have different levels of humidity. This will cause the amount of
flour required to vary. The age of the flour also affects the amount
of water it will absorb.
You mention that you have existing starters. Did you convert the one
you used to the same hydration she used in her starter? Maggie is a
fan of relatively firm starters, 62-65%.
All this said, when I tested this recipe I too had to add flour. I
did not see big expansion in either the bulk fermentation or the
proofing. I did get great oven spring and the finished bread had a
nice open crumb. It can be seen here:
http://www.kyleskitchen.net/collision_course.htm
Hope this helps.
KyleW
www.kyleskitchen.net