"Deciphering papal ciphers from the 16th to the 18th Century" by George Lasry, Beáta Megyesi, & Nils Kopal, now included in Volume 45 of Cryptologia, studied many ciphertexts in the Vatican archives systematically and identified no less than 16 keys. I should have mentioned this when the paper was published online in June 2020. Until now, I mentioned it in "Unsolved Historical Ciphers" only as a footnote to "New Vatican Challenges." Now, I mentioned it in a separate entry "Papal Ciphers from the 16th to the 18th Century."
While it was described as "The alphabet is expressed by figures or symbols, small words by a combination of figures and letters, and proper names by pseudonyms ..." by Green, I found that letter pairs are also used in the substitution alphabet. (The two pages I referred to did not contain code for small words or pseudonyms.)
I also found an additional example of what I call the Second Cipher between Charles I and Henrietta-Maria (Aug. 1642-Jul.1643) in Harley MS 7379, f.86. The letter is dated 9/19 January, but the year is not given. I think it is 1643. This is partly because of use of this very cipher and partly because the letter begins by acknowledging receipt of the King's letters of 22, 25, and 28 December. Considering that the Queen was still in England in December 1641, the dating of this letter at January 1642 seems unlikely.
I post the following provisional (not very accurate) transcription in the hope that someone may help establish the date of this letter.
Harley MS 7379 f.86
Henrietta-Maria to Charles I, 9/19 January
Mon cher coeur jay receu trois de vos lettres
en mesme jour une datee du 22 decembre lautre
du 25 et 28 dans lune desquelles vous me mandes
laisidant* qui est arive a ma lettre qui e s
t o i t d a n s l a c a n e
jan suis bien fachee car il y avoit beaucoup
de choses de dant elle estoit je ne me puis plus
souvenir de ce que estoit jay fait tout les
diligances que tous ques desiree e n [p48] et
jatans w:m: t o u t l e s
i o u r s mais il d o n n e fort
p e u d e s p e r a n c e d e
F: je vous avois desja escrit par lordinaire
de devant le dernier comme javois selon vos
ordres e n u o y e en F: pour
d e s a r m e s comme  avoit
comande a  sest pour quoy il fault que vous
ayes soing de envoyer l a r e n
a f o s t e r et lordre ou il l e
s f e r a t r a n s p o r
t e r car sest luy qui en prand le
soing pour mon voyage vous naves que
faire de man courager car je suis ases
mepariance de partir i l n i a
que l e u e n t qui e n p
e s c h e d e p a r t i r
jespere que s e r a s i
t o s n8[with] 189 que 260 remeteray a
respondre auec lettres de p a r b o
t c h e seulement je vous prie de
dire a 189 que tout se quil ordonne sera
fait touchant l e P: Tre: je serois bien
ayse de savoir les particuliarites sest pour
quoy je vous prie de me les envoyer a
226[Ven:] car il est necessaire que je le
sache pour votre service je nay plus
rien a dire et espere que s e s t e
l e t r e sera l a d e r
n i e r e que o r a d
e m o y de Holl: a dieu mon cher
cocur sy sette lettre est prie il gora
a desifre ce 19/9 janvier
lette a 113 que je ne luy escris
point mais quil asure
et a 82 aussy.
The Vigenère cipher as known today is not what Blaise de Vigenère proposed in his Traité de Chiffres (1586). The scheme known as "the Vigenere cipher" today became popular by Dlandol (1793). Vigenère's name was associated with it by Kerckhoffs (1883) in a classified description of polyalphabetic ciphers. While Kerckhoffs did not mean to identify the inventor, his work was so influential that the term "Vigenère cipher" took root in the vocabulary of cryptology. See my new article "Who Made "the Vigenère Cipher" as Known Today?" at Academia.edu. (I may have misunderstood the term "Published Papers" at Academia.edu. So, this is uploaded as "Draft.")
I made additional remarks in "Did Beaufort Really Use the Beaufort Cipher?"
Following the previous post, I acquired a copy of Chinese Telegraph Codebook. This time, it is a 1941 edition from Commercial Press, printed in Hong Kong in 1968. Again, it is substantially the same as what I already described, but I added seven images in "Chinese Telegraph Code (CTC), or A Brief History of Chinese Character Code (CCC)" (and a full version in Japanese).
Many Chinese telegraph codebooks are on sale on Chinese websites (much more than Japanese telegraph codebooks sold on Japanese websites), but I cannot order them from Japan (at least because I cannot read Chinese). The other day, I found some Chinese codebooks are available from secondhand booksellers in Japan. I was so glad of the findings that I ordered one from 1916, though I was aware that it was one I've seen on the web. As long as I got a copy, I added pictures to "Chinese Telegraph Code (CTC), or A Brief History of Chinese Character Code (CCC)" (and a full version in Japanese).
The picture below shows the oriental binding, with two pages printed on a folded sheet (Wikipedia).
This was not the case when I acquired another codebook which I think is from the 1930s (reported here).
I uploaded a new article: "Did Beaufort Really Use the Beaufort Cipher?".
The Beaufort cipher is a variant of the Vigenere cipher, so called because it was invented by Admiral Francis Beaufort. But it appears that Beaufort himself never used the cipher himself. The cipher Beaufort used in letters to his brother or his secret diary was more primitive.
The article also discusses when the Beaufort cipher was published. (I was induced to check this when I read Lewis Carroll may have known of the Beaufort cipher.) Some say it was published in 1857, but considering that Beaufort died on 17 December 1857, this dating does not seem to refer to an actual date of publication. Maybe, some writers simply quoted the year of the admiral's death. At least, it was only after the (re?)publication in 1870 that the Beaufort cipher became widely known. (The version published in 1855 on a magazine was actually the conventional Vigenere cipher, as pointed out by Franksen.)
I checked my usage of the term "two part" for this kind of arrangement. In most of the cases, I used the term with a reservation that the arrangement is not completely random. But I'm going to add a note about this in one of my previous posts: "Cardinal Mazarin Used Two-Part Code ".