I had to comment on this. I know the comics always put Clark's birthday as February 29, but I can't see this happening. People who are born on leap days are always given special attention, especially when it’s a leap year. Attention on when their son was born would be the last thing the Kents want... Just my two cents!
It's been awhile since I've seen the episode, but I believe that in "Never On Sunday" Clark actually said his birthday was February 28, given there was no February 29 in 1966. I don't think the script was ever changed.
Oh, I thought you guys would get a kick out of this. This is actually the way that my roommate likes to tease me. She's the only one who knows that I like (am obsessed with) LNC. We'll be in a group of friends, and she'll randomly say that there was no February 29 in 1966. I'll be grinning and blushing like crazy, and she's the only one who knows why.