Second, when Michael and Kay are dancing at Anthony’s party, she says, “You said the Corleone Family would be completely legitimate in five years. That was seven years ago.” Since the party is set in late 1958, it means that Michael and Kay were married in 1951. And since Michael told Kay in GF that he’d been back in the US for “a year, maybe longer,” he must have left Sicily in 1950.
This is perhaps the first time that I'm defending the logic of GFII.
"That was seven years ago", may refer to another discussion between Kay and Michael, not necessarily their meeting in New Hampshire. Also, perhaps Kay's memory might be wrong. After all they were drinking a lot that night.