For Two Special Boys

I came across these nickname etymologies and thought they were interesting.  Who knows how accurate these things are.  My husband, who is a bit of a linguist, dislikes amateurish use of inaccurate etymologizing, especially when used in Biblical argumentation.  But since this only for fun, I hope he doesn't mind too badly my repeating of etymologies the accuracy of which is unknown.

Henry is one of my Godsons and John is my youngest son.  Have fun boys.

Why is Hank short for Henry?
The name Henry dates back to medieval England. (Curiously, at that time, Hank was a diminutive for John.) So how do we get Hank from Henry? Well, one theory says that Hendrick is the Dutch form of the English name Henry. Henk is the diminutive form of Hendrick, ergo, Hank from Henk. Hanks were hugely popular here in the States for many decades, though by the early 90s it no longer appeared in the top 1,000 names for baby boys.

Why is Jack short for John?
The name Jack dates back to about 1,200 and was originally used as a generic name for peasants. Over time, Jack worked his way into words such as lumberjack and steeplejack. Even jackass, the commonly used term for a donkey, retains its generic essence in the word Jack. Of course, John was once used as a generic name for English commoners and peasants, (John Doe) which could be why Jack came became his nickname. But the more likely explanation is that Normans added -kin when they wanted to make a diminutive. And Jen was their way of saying John. So little John became Jenkin and time turned that into Jakin, which ultimately became Jack