Friends are friends.
They don’t necessarily use formalities unless they want to.
When I was young the bishop and his fellow seminarians were all great buddies who’d been in the air force from WWII. They all had call signs.
Now, if you know anything about call signs, you’d know that they are less than flattering.
The Bishop called his friends by the names he knew, and they called him by the name they knew.
I imagine that wouldn’t change today.
