Try New Shit All the Time - trial and error.
I have found that there is some sort of weird assumption that certain things can't be changed once a decision is made. I guess it has to do with looking bad, or some weird reverence to not trying something new.
I've learned over the years to challenge that type of thinking when I come across it. For example, I have had several, but not many, cases where a specific employee was so talented that I was constantly unable to put them in a competency level, which is what we used to determine salary and equity. They were such fast learners that within months they had gone from a junior employee in my mind to an "I can't live without them" employee.
What do you do?
The answer is simple. Pay them more and let everyone know that you are doing so. Don't shy away from it. If you discover a rock star, pay them. Your employees, your board and your conscience will support you.
Further, if you put someone too high and you realize your mistake, tell them and move them down. I've done that too and the employees, including the one I moved down, agreed with me and applauded my bravery for admitting that I screwed up.