It's funny you mention that. Just yesterday I made a graph of how many accounts were created each day since the beginning of reddit. It's very clear which day Paul mentioned reddit in his essay, because there was a 3x jump in signups that day. More importantly, it never receded from that level. I like to think this is because people kept finding his essays.

Most everyone in the technical subreddits would know about pg and YC. After that, most people who identify strongly with the community would probably know its history.