this one page said Larry Mondello was called Frankie early on.
I don't remember that.
What season was this, I would like to watch it.
I think it might be in error.

Larry Modello, red-haired, freckle-faced, whiny-voiced, potbellied perpetual loser, is also Beaver’s best friend. Called "Frankie" early on, Larry never, ever looks really happy, but he comes closest when he’s got something working in his jaws. He’s most often remembered as the kid who is always digging something out of his pocket to eat, usually an apple. In fact, he probably eats more apples than Mr. Ed.

Larry’s father is always "away on business," often in Cincinnati, for some unexplained reason, and it is left to Mrs. Modello to raise Larry and his older sister. This task proves far too great a strain on his mother, and as a result, she is a very nervous, worried woman who can’t wait for her husband to get home to "get to the bottom of things." To hear Larry tell it, his father’s way of getting to the bottom of things is via direct pressure to Larry’s bottom.

There's a Frankie in the pilot episode It's A Small World, but he was played by Harry Shearer.

Maybe thats where they got it.
Then this other one said Larry was seen in season 4 in a few episodes, "but almost like an anonymous friend"

Rusty did leave the show, obviously. But apparently not that suddenly, as he did appear in just 2 season #4 episodes, but almost like an anonymous friend intead of good ol' Larry.

I wonder what episodes that was, as I don't seem to recall him being an anonymous friend.

OK, he is in,"Beaver's Freckles" where they were washing Lumpys car.
"Beaver's Big Contest", when Beaver wins the car, they are sitting in that box, with a old buggy wheel, as a steering wheel, pretending to drive.
According to this page, that is the only 2 in season 4.
http://en.wikipedia.org/wiki/Leave_It_to_Beaver_%28season_4%29