I'm familar with the names you've mentioned, I know for sure there are alot of Chaco and Leon Guerrero family. In the old days, when families had the same last name, another name was given. The name given is determined by what your family in known for, where you live or where you came from. Here's my example: My moms last name is "Santos". Her family is from Agana. But, because there are so many Santos, The given name is Bee-big. I'm not even sure of the spelling, But that's how it's pronounce. "Bee-big" is the sound of a whistle. Her parents home was close by to this place that makes the whistle sound. It's kind of funny because Bee-big does'nt sound anything like a whistle. I won't complain because some names are pretty humorous and alot worst then the ones my family inherited. I think "Chaco" might be the nickname of your chinese grandfather and because he was of chinese decent, it might of been a way to determine which "Leon Guerrero" family he came from . I'm not sure really, just an idea. I will check it out for you and let you know what I find out.