In any projection about how an NFL team can improve from one season to the next, the focus tends to be on new blood, i.e., players possibly arriving in the draft or free agency.
It’s understandable. Nothing is more tantalizing than an unknown quantity looming on the horizon.
In the end, though, many holes are filled in less exciting fashion, by guys already on a team’s roster. Pro football’s economics all but demand it, for the simple reason that the salary cap’s limitations preclude teams from “buying” the solution to every issue. They have no choice but to “promote from within” at times.