yup, perf grade fluctuates. Not every panel is going to guarantee your A/B grade every year as a GEO4/5 KP. Some will 'spread the wealth over the years'. PB, just like the mid year and year end variable payments, fluctuate. You can't do financial planning based on that even though your total comp in a 'good' year may be stupid high.

At SEO1, it is not terribly difficult to hit C grade every year if you are responsible and meticulous, and know how to work smart. Forget the As and Bs, your base salary is already higher. The As and Bs come unexpectedly and should just be treated as occasional nice surprises.