There is a big advantage in having a coaching staff that has been intact for a while. On the other hand sometimes coaching changes can result in some immediate improvement on one side of the ball or the other.
Examples: Oklahoma made four asst coaching changes include new OC Lincoln Riley and moved DC Mike Stoops off of the field and into the box (very emotional on the sidelines). Should be some immediate improvement across the board in my opinion.
Texas A&M landed DC John Chavis who I think is the best DC out there and has years of SEC experience. Again, I look for immediate improvement on that side of the ball.
Here is a list of schools where the HC, OC, and DC have been together at least 3 years. The number in (X) indicates how long each have held their current positions at their current school:
ACC
Virginia Tech – HC (29), OC (3), DC (21)
Virginia – HC (6), OC (3), DC (3)
Miami Fl – HC (5), OC (3), DC (5)
NC State – HC (3), OC (3), DC (3)
Big 12
Oklahoma St - HC (11), OC (3), DC (3)
Kansas St – HC (7 currently – 24 total), OC’s & & 18), DC (4)
AAC
Navy – HC (8), OC (8), DC (8)
Memphis – HC (4), OC (4), DC (4)
Temple – HC (3), OC (3), DC (3)
Big 10
Iowa – HC (17), OC (4), DC (4)
NW – HC (10), OC (8), DC (8)
Minnesota – HC (5), OC (5), DC (5)
Illinois – HC (4), OC (3), DC (3)
Purdue – HC (3), OC (3), DC (3)
CUSA
Mid Tenn St – HC (10), OC (5), DC (4)
Old Dominion – HC (7), OC (7), Dc (3)
Marshall – HC (6), OC (6), DC (3)
U.T.S.A. – HC (5), OC (4) DC (6)
U.T.E.P. – HC (3), OC (3), DC (3)
Independents
B.Y.U. – HC (11), OC (3), DC (11-also HC)
MAC
Ohio – HC (11), OC (11), DC (11)
Akron – HC (4), OC (3), DC (4)
W. Michigan – HC (3), OC (3), DC (3)
Mountain West
Air Force – HC (9), OC’s (9) & (5), DC (3)
S.D. State – HC (5), OC (3), DC (5 – also HC)
Fresno St – HC (4), OC (4), DC (4)
Pac 12
Arizona St – HC (4), OC (3), DC (4)
Arizona – HC (4), OC (4), DC (4)
SEC
S. Carolina – HC (11), OC (11 – also HC), DC (4)
Ole Miss – HC (4), OC’s (4 & 4), DC’s (4 & 3)
Kentucky – HC (3), OC (3), DC (3)
Sun Belt
Georgia St – HC (3), OC (3), Dc (3)
Appalachian St – HC (3), OC’s (3 & 3), DC (3)