Oh yeah, something like that happened at Everest Challenge. There was a guy that finished a little behind me on the first day, but he was struggling to keep my wheel and he just fell apart on the last mile. On the second day I dropped him easily on the first climb, but somehow ended up passing him again later in the day (I hadn't stopped). He didn't speak much English, but I asked if he did the whole thing and he said he did. There is no way he could have gotten back ahead of me!