Former Tottenham coach Jol would have cost £8.4m in compensation if Fulham had sealed a deal to recruit the Ajax manager last week.
Yet if the Craven Cottage club had done the deal before July 1, the pay-off to the Dutch club would have been just £1.5m.
Jol had a clause in his contract which allowed him to move to a Premier League club between the June 1 and July 1.
Ajax managing director Rick van den Boog said: "We did not want to lose Jol."