I understand that only 18 tournaments (19 if qualified for ATP Finals) are considered for ATP rankings of which 4 grand slams and 8 masters (excluding Monte Carlo) are compulsory. If a player fulfills the commitment of 4 ATP 500 (counting Monte Carlo if he plays), his best 6 results from other tournaments are counted.
But currently (16th March 2018), I see 7 tournaments (apart from compulsory tournaments) are counted in Marin Cilic’s Rankings. It includes Monte Carlo, 3 ATP 500 and 3 other tournaments. Is it not violating the rule?
His ATP Rankings Breakdown is here. And here is Internet Archive snapshot from March 2018.