Since I had this and the last year's seniority lists in hand and not much else to do, I ran some numbers.
This year's attrition rule of thumb looks like this:
First year of service - 185
Second year of service - 80
Third to within a year of flow - 60/yr
Year before the flow - 40

Do what you will with that. I'm mostly leaving it here to compare the numbers next year.