No potato unless it's day 3. A cucumber and a potato are 100% different in nutritional makeup, thus a potato, technically a tuber and pure starch/carbs is not the same.
Winter squash in light moderation is OK. However once again not the same in nutritional makeup as regular veg like cucumber. Although after the diet a very healthy good carb and veg.
The principle, is truly a long story. Basically it breaks the plan up going into day 5.
What time of the day do you weigh yourself?