I was on Sitcoms Online today and listened to the 1959-1960 (third season) ending clip. It has a whistled first verse. It is in Season 3 now, and I have not heard that one once, and I have seen every episode. They are using the 1961 (forth and fifth season) ending.

Why would it do this. Is Sitcoms Online wrong about it being 1959-1960, wrong about the one they are using from 1961, or is it something else?

Great observation, #5, but in all honesty I hadn't noticed it.