As I'm sure you're aware, 'back in the day', the three letters referred to the registration district. In the face of it, this makes the chances slim because the two other 100s would have to travel in from their respective other counties.
On the other hand, big cities would have dozens of three letter sets all applying to the same registration district, and the lower numbers on each sequence would be the most likely to recur. So, if you live in a city, the odds of this coincidence aren't so low.