What are the odds?

I have lived in my apartment for a year and a half. I still get mail for 4 or 5 past tenants occasionally. Some of it "real," but mostly credit card apps, advertisements, etc. However, I find it interesting that past tenants have my same last name. Two in fact! What are the odds? Now, granted, the two former tenants could have been married and living here at the same time. None of the mail comes with both of their names on it, so I have no way of knowing, but that is possible. There are 641 people in the city of Houston with my last name. But I only know one of them...and we're not related. So what are the odds that two of them formerly lived in my current apartment?

Weird...