When the joke was first made (Mr. Burns using the phrase), it wasn't "common" knowledge, but it was a known thing. Like one of the "fun facts" you'd find on a cereal box, or in between segments of a TV show, or as a Jeopardy question.

I remember seeing the episode and understanding the joke... it was just meant to make Mr. Burns appear *really* old.

Maybe I just had a ton of useless/esoteric knowledge as a kid -- that's likely too.