I think you would remember if you were at a history making event or not. I, for example, was not there when the Berlin Wall fell
Just so you know, while the civil rights movement was an historical event, a single march in the thousands that took place over the years was not so much so. Plus, there was a real civil rights march that Romney was in, at the place he says it happened — the only mistake in the narrative is that MLK wasn’t actually IN that march, even though it was a Martin Luther King Freedom March.
It’s an easy mistake to make in memory years later.