Quoting K. P. Walsh:" I don't feel that it sounds like an incomplete name. I don't like the names that are short for Allie and my grandmother's name was just Allie."
I wondered why my friend only gave her daughter the name Ally only as well. She said no matter what the full name was, if the nickname was Ally they would of always called her just Ally anyway.
But Alley is my friends maiden name, her dad was dying when she was pregnant, died shortly after her DD was born, and she couldn't make her dad's name girly at all. Wanted to honor him somehow, so they did Ally, instead of Alley.