Michael I think that is a great point...If Columbo's creators..Levinson & Link...did not give him a name then he has no name.......sort of like Frankenstein...the monster had no name!!
I suppose you could also say since Columbo has become a developed characer himself . . . and he has not indicated he has a name preference, we don't know what it is. It must exist; it hasn't been revealed by anyone who knows. I don't suppose Mrs. Columbo revealed it? Of course, many don't acknowledge that series.