Standard nicknames that have no apparent resemblance to the full name

I’m not sure which one is specifically a nickname for the other, but I know several people (including a cousin) who will respond to either Teddy or Sal. In fact for at least two of them (including my cousin) I couldn’t tell you which one is their actual name.

Pepe. Pepé is le Pew.

The P.P. is also many centuries older than the 20th, it’s found in almanacs from the 16th and in statues before that.

Teddy or Sal? My guess would be that his real name is Salvatore. I can see how you could get to either from there.

It might have been nonsense in this particular case, but it’s accepted that generally speaking there are several nicknames that are derived from “brother,” including “Bud,” “Buddy,” and “Bubba.”

“Baby M” was named “Sara” by her biological/genetic mother and “Melissa” by her genetic father. When the father’s name was chosen as her name, her mother dubbed her “Sassy,” and never called her anything else.

This is also true in Czech - Josef = Pepa or Pepik. I wonder if this has something to do with the padre putativo story.

Neither of those are nicknames, they’re foreign names from the same source.

Hebrew, Yaakob, IIRC. Translated to Jacobus in Latin.

Jacobus became Jacomus, which became James.

Jacob is just delatinized.

Diego ultimately comes from St James (that is to say Sant Iago) - some say Diego comes from Didacus, but I’m in the camp that believe it’s the other way 'round - when someone who didn’t know the derivation decided that a Diego’s name needed latinization, he settled on Didacus.

I’ve known several Katherines who were nicknamed Kacky.

Likewise in my family: my grandfather and uncle are Roberts, but it’s Grandpa Bob and Uncle Rob.

Skip - II (named for grandfather)
Chip - Jr.
Trip - III

I’m technically a Skip but have never been called that.

Well, my latin is absolutely rusty, but I’m reasonably sure that the initials of assumed father in Latin are P.P. as well - actually, those medieval statues with P.P. engraved on the base would have them as the Latin initials. It’s got to be something like putativus pater (with appropiate declensions).
My mother (she who recognizes the names and can give mini-bios of extremely obscure saints) says that Paco comes from Pa.Co. Padre de la Comunidad (pater comunitatis), Father of the (Franciscan) Order. Statues of St Francis Assissi would be recognizable either for the wounded hands, for being with a wolf and a lamb, or for having Pa.Co. on the base. You’ve got a statue of a generic Franciscan, no idea who he is, and want to have a St. Francis? Why, just engrave Pa.Co. on the base and you’re done! (And yes, changing a statue to be someone else was done - the statue known as “St Anne the New” in my hometown started life as an unbearded St Joseph with Child)