I think the designer accepts that this is going to be pretty subjective:

"Of historical interest" is not a fixed measure. History is subjective. A historian chooses what is "interesting" and what is "not interesting" based on the topic he or she is writing about, his or her own biases and the quality of the sources available.

Must say though, the numbers aside — I've always considered myself a reasonably well-versed Irish person and I've discovered some interesting people through this little project. :)