After 25 years of checking women, i have come to the conclusion that except in the case of preterm labor, you just need to know if the cervix is thick, thin or somewhat effaced.
I tend to use thick, 50%, 80% for those that feel thin but not paper thin and 100%.
What does it really change in your management?
Don't sweat it, it is all subjective anyway.
We have one MD who told me he has caliper-like fingers and can tell the difference between 35 and 40% effaced. I say hogwash