I've been reading through the extra pieces in the Norton Critical Edition of NA and there is yet another mention of Richard! This one is JA's "The History of England" written at the tender age of 15. It's delightful and mocks everyone and skips over great gobs of history. But there is a funny passage about King Richard III (-who was an awful man from what I've read. To say it tamely). And I quote:

"The Character of this Prince has been in general very severely treated by Historians, but as he was a York, I am rather inclined to suppose of him as a very respectable man."

There is a footnote attatched to this by the editor. She comments that the above quote is very like the one that you noticed in NA- "a very respectable man though his name for Richard."

Yes, it was a family joke and it must have been a very long stretched out one! I wonder what spurred that joke on for them. I wonder if it could have started with JA's "The History of England"!