Did Edmond not know how to count?
He was at Albert's 16th birthday party; did it really never occur to him to count the months back and figure out that Albert was conceived right around the same time he was arrested? Mercedes told Fernand that Albert was premature to cover up the truth of his parentage, but there would have been no reason for anyone to tell The Count of Monte Cristo, "Hey, Count Mondego's son was born a month early!"
I find it hard to believe he wouldn't have at least suspected Albert might be his.
"As long as there has been one true god, there has been killing his name."