Body Parts 1 tips & notes correction
Regarding this statement: "They also possess a body part that humans do not: the qIvon, about which little is known besides its name and the fact that some (or perhaps all) Klingons seem to have more than one."
I would like to submit the following for consideration: https://memory-alpha.fandom.com/wiki/QiVon — "According to the Star Trek Encyclopedia (3rd ed., p. 393), this was the Klingon word for 'knee'." http://www.kli.org/tlhIngan-Hol/2006/August/msg00052.html — "The Okuda 'Omnipedia' identifies 'QiVon' as being another word for knee."
Okrand is quoted later on the 2nd link, not actually confirming or denying this definition, but would these reference materials not be considered canon?
No. "Okrandian" canon is not Star Trek canon. If Okrand didn't invent it or approve it, it's not canon. Here is what Marc Okrand has to say about the qIvon in The Klingon Way:
If the qIvon is cold, the blood is hot.
bIrchugh qIvon tuj 'Iw.
It is not clear what a qIvon is, aside from the fact that it is a Klingon body part, so the real meaning of the saying is a little obscure. It probably means something like "Even though some parts of the body may be cold, a Klingon's blood is hot" — that is, he is ready for battle.
Meanwhile, the Klingon word for knee is qIv.
Okrand will often retrofit things that are said in Star Trek into the language. But not everything has been retrofitted.