Season One Goof
Watching this series again, this time on Netflix... In episode 8, Sam leaps into April 1953 but he's not born until August of that year, screwing up the whole "within his own lifetime" bit. I suppose by this point they hadn't yet gotten Sam's exact birthday down.
Edit: This happens again in Season 2 in episode 3, Sam leaps in August of 1953 but a few days before he was born.