How did Ipswich manage to go from league one to potentially the premiership in one season.

This suggests their recruitment department knows what’s it doing!
he as had the squad ( majority) as a unit for nearly 4 years and turning them into his team and playing his way ( bit like JE wanted to do but didn't have the right players) add into the mix a sprinkle of seasoned pros & solid loanees & you have a really good squad....they had a 5 year plan and it worked
 
Last season Leicester and Leeds showed us how overspending by 200m got them relegated to the Championship.
The beauty of having the most competitive set up in the world had Maidstone from National league South go to Ipswich and win.
Unusual things happen to a few whilst the rest go about life as you would expect them to, without having false expectations
 
Carlisle did it from league 4 to league 1 in 3 seasons, then got relegated back to div 4 again if my memory serves me right
I think you’ll find after consecutive promotions from Division 4 to Division 2 (Championship today) Carlisle remained there for several years before they made it to Division One.

Relegated to Division 3 in 3 seasons then Division 4 sometime later.

Northampton Town on the other hand went from Division 4 to Division 1 in 5 seasons and back to Division 4 in just 4. Now that was rapid!
 
Was it Carlisle or Swansea that nearly went out of the league until late in the last game?
Did the goalkeeper score?