To achive Club Legend you need to "Reach your objective with the same club 5 times".
I´ve managed Palermo four times and every time I´ve managed to achive the objective. First time it was in june 2011 with US Palermo, second time with Palermo in november 2011, third time in september 2015 and for the four time this april (2017).
When I look into my Achievements it says that I´ve managed to reach my objective only three times. I saw on this forum in Common Questions "that some achievements were introduced on 14th October 2014. Some achievements only start counting after that date. Cup achievements are one of them, so only cups won after that date are taken into account" but if this is true then I should´ve only 2/5 for club legend achievement.
I'm pretty sure that Palermo is the only team I've coached four times...