The uncertainty factor being that there is continued ongoing hiring of people with less than 25 years - even less than 20 years remaining before they hit age 25. That may even increase as those lured to the regionals by big DEC bonuses begin to see their contracts expire and 43-44 year old military retirees start their second career. Remember, everybody in your INTRO class who is senior to you bidding on base and equipment will be at mandatory retirement before you will, and everyone in subsequent classes older than you as well.

The number of people retiring before you isn't a static figure just because that's what it is when you get your seniority number, only the number of people senior to you. So actual number retiring in those more distant years will be greater than currently projected.