I know earlier this week Kotaku said they didn't like the "Gump" effect that AC3 had (as in Forrest Gump) and Patrick some what shared these feelings on the Bombcast. What I find humorous though is that there is a real figure by the name of George Hewes who often has been referred to as the Forrest Gump of the revolution because even though he was just a plain old guy he was present for numerous monumental moments. So it's not ridiculously far fetched especially if you factor in the fiction that in AC you have secret organizations in play with presumably inside info.
Secondly it's a videogame, it's pretty dumb to be playing a game where 2 secret factions have been warring for centuries and you go back in time through your ancestors memories (or some shit) and the thing that takes you out of it is going "Wait a minute.... he was at both of these historical moments? Hurmph, I think not. "