singular possessive (my King Charles's head)

In a footnote to his recent review of Human Smoke, David Gordon used the expression “King Charles’s Head.” I had no idea what that meant, so I looked it up. Once I knew its definition, I wanted a way to communicate it to any other readers of the Mises Review who shared my ignorance. The problem is that most free dictionaries online are ugly and full of ads. So I decided to create an entry at Wiktionary.org. I created the entry as “King Charles’s Head,” exactly as Gordon used it. One of the Wiktionary regulars corrected and expanded my entry. Here’s the note he left me:

Sorry, I made a mess of King Charles’ head. Please feel free to improve that entry. King Charles’s head should be marked as an {{alternative spelling of}} or {{misspelling of}}. But King Charles’ Head with a capital on Head is incorrect. Yours Conrad.Irwin 20:39, 9 May 2008 (UTC)

I changed “Head” to “head” in the review, but as I wrote the wiktionarian (perhaps in the wrong place?), I don’t understand his stripping away the ‘s from King Charles’s name:

Conrad.Irwin, thanks for catching the spurious capital and thanks for expanding the entry. Thanks also for teaching me some wiki syntax; I’m new here, as the rest of this message will no doubt reinforce.

I’m confused about your change in the spelling of the singular possessive, from Charles’s to Charles’.

I see 3 arguments for the former:

1. The reference is originally to Charles Dickens’s David Copperfield, where it is spelled “King Charles’s head.”
2. The Chicago Manual of Style says, “The possessive of a title or name is formed by adding ’s {Lloyd’s of London’s records} {National Geographic Society’s headquarters} {Dun & Bradstreet’s rating}. This is so even when the word ends in a sibilant {Dickens’s novels}…”
3. The much more accessible Elements of Style says the same in its very first rule:

Form the possessive singular of nouns with ‘s.

Follow this rule whatever the final consonant. Thus write,

• Charles’s friend
• Burns’s poems
• the witch’s malice

This is the usage of the United States Government Printing Office and of the Oxford University Press.

Is there a Wiktionary style guide I should be referring to instead?

Thanks again.