You may get good bud survival and you can get a sense of what the year may deliver, but the canes that come out may have poor or small flowers, so you adjust your expectations. Or great flowers but heavy rain disrupts the flowering stage and you get poor fuirt set. Or maybe fruit set is great but you get powdery mildew attacking the vines or hail, or insects, cold weather or drought etc etc etc.
Every stage through the growing season has its own potential pitfalls. This year we already have rain and fungal pressure as a cause for concern. Don't get me wrong we love the rain, just not when the flowers are blooming - and that is when we got a pile of it this year. So some of the vines experienced poor fruit set, notably L'Acadie Blanc and Ravat 34. Both of these were the last to bloom and were blooming just when we got alot of rain over several days.
On the other hand, some of the other varieties such as Leon Millot were blooming a week earlier and we have good fruit set on them. The picture here of the Leon Millot is from July 1st.