So, Aleksandr-Aleksasha. The dropping of "Alek" is the only inconsistent part, on par with Agrippina-Agrusha-Grusha.
It's archaic, used in Peter I times. Modern one is Kolya
One of the potential diminuitives for "Aleksandr" is indeed "Lesha", although I think it's more common as a diminuitive for "Aleksei"?
I'm bad with names to begin with, so I usually make a chart to keep side characters straight.
To add confusion, the choice of which to use is usually context-dependent (time period, age, status, situation, relationship between characters) but sometimes the author will switch between, say, title and surname within the same paragraph simply as a matter of style or to avoid repetition.
I've been reading Tom Clancy recently, and that's basically the Jack Ryan books. Somehow, "Jack" is actually a nickname for "John".
That has never made one iota of sense to me. The whole "Dick" / "Richard" thing makes more sense than "Jack" / "John" to me (and it's nonsensical, too).
- Jehan (Old French form of "John") -> Jan
- Jan -> Jankin (diminutive)
- Jankin -> Jackin
- Jackin -> Jack
This does give me a reason to preserve some fact about one of my favorite cats ever in perpetuity (given the similarity of the John / Jack transition to Joe the Cat's life).
A friend's cat (who I knew as Joe the Cat) went from being called "Ivy" to "Joe" over the course of the cat's 15+ year lifetime by way of being called, successively: Ivy --> Jivey --> Jive --> Java --> Joe
Joe was calm and compliant, and arguably "a good kitty" (albeit I only knew him late in his life). My friend once described Joe as being more frantic in his youthful vigor but being "pacified through years of routine and systematic abuse".
No, my friend and his and his family didn't actually abuse Joe the Cat. He was much loved. I get to use the phrase "years of routine and systematic abuse" in my life (as often as possible!) now, though (often referring to my experiences with various pieces of software).