I am really surprised that no one picked up on my earlier comments.
The whole survey is destined to fail.
A person who “came in” in 2010 cannot possibly have done 40 years because there has not been 40 years since then. So the people who came in longer ago will on average have stayed in longer before leaving and the people who recently came in and left will have on average left more quickly.
It’s like saying that people born in the 60’s live longer than people born in the 90's because they are older!
Or if I am losing the plot please tell me.