Itchiford isn't Itchy's last name.  In ADGTH part 4 where Charlie introduces Itchy to Anne-Marie, he doesn't say Itchy Itchiford.  He says, and I quote, "And this is my associate, Itchiford "Itchy" Dachsund."  I'm not sure on the spelling, but that's what it sounds like.  Turns out, Itchiford is his real first name, not his last name.  If you doubt it, look up "all dogs go to heaven part 4" on youtube and click the first video.  Wait until Charlie introduces himself and Itchy, and you hear it.  That is all I have to say on the matter.