You're right, Sonny. Here's what Harlan Lebo says in his definitive "The Godfather Legacy" (p.251):

"During the six weeks of filming at Cinecitta [Rome]...the crew erected massive sets on four enormous soundstages. The largest was Michael's lavish New York penthouse apartment; others included an Atlantic City luxury suite that was machine-gunned to pieces in a meeting of Mafia dons."