I still haven't really been able to figure out how this works.
Two seasons ago, I hired this young OL-guy,
https://ags.myfootballnow.com/coach/528. 78 rated, 30 years old. Match made in heaven!
Since then, he's went down, a bit up and then more down. Now being 32 years old, some solid experience under his belt, but worse.
This guy
https://ags.myfootballnow.com/coach/627, from the same "batch" of young guys I tried, has developed well, on the other hand.
This guy
https://ags.myfootballnow.com/coach/538, my DL guy, is now 33. Just hired him. The first 2 years in the league, he was unemployed, but improved. I guess you can just go through all the young coaches and see who improves. I guess it'll take a loooong time for some of them to be actually useful though.
So my guess is, that it's just a bunch of tiresome "grinding" through the lists, to find up-trending coaches.