So I guess I don't really have grounds to criticize.
Jo just kind of happened though. When I was in elementary school we had 6 Jennifers in our classroom. Teachers basically renamed us.
Jennifer,
Jen,
Jennie,
Jenna,
Jo,
Jem. I got
Jo because my fn/ln initials are J.O.
Stuff like
Sammy,
Nicky,
Charlie,
Danny... eh. I don't hate them, but they aren't something I'd particularly want to use.