Oh man, now that I think about it, one of my main OCs was a repurposed RP character! And that was...crap, first year of high school, so 15 years ago.
...damn, I feel old now...
...uh, yeah. That's the danger of me RPing. I have four or five of those really, really old guys and gals floating around. They mostly get spun out of characters I make up on the fly for realtime one-on-one RPs. Most of the new ones have a decently fleshed out past, but all of the super old ones have very detailed backstories. I like to think of it like writing a non-fiction biography for a person who doesn't exist. Got to dig deep and research and make everything line up year to year. Which is tough going, when you've got OCs floating around who are 300+ years old.