Cipher Letters to Charles I of England (1645) in the Parliamentary Archives

The other day, I ran into a blogpost of the Parliamentary Archives: Katherine Emery (2020), "Cracking the code: Love, war and letters". This made me aware that some images of cipher letters to Charles I are available at the Parliamentary Archives (and reminded me of ciphers in the British Library I had noted before for future study).

(1) Letter in "Cipher with Ministers in Oxford (Spring 1645)"
Nicholas to Charles I, 22 May 1645 (Parliamentary Archives)

(2) Letters in "Third Cipher between Charles I and Henrietta-Maria"
(2-1) Jermyn to Charles I, 12 May 1645 (Parliamentary Archives) *This record cannot be reached by the search terms such as "cipher", "decipher", but the ID in the official blog readily led to the relevant page.

(2-2) Henrietta Maria to King Charles I, 6 January 1645 (Parliamentary Archives)

(2-3)Henrietta Maria to King Charles I, 13 March 1645 (Parliamentary Archives)

(2-4)(Jermyn?) to Charles I, 21 April 1645 (Parliamentary Archives)

(3) Letter in "Second Cipher between Charles I and Henrietta-Maria in Holland and the North (Aug. 1642-Jul. 1643)"
Henrietta Maria to Charles I, 27 June 1643 (Parliamentary Archives)

(4) Letter in "Cipher with Prince Rupert, Digby, and Ormonde (1644-1645)" (formerly called "Cipher with Prince Rupert (Summer 1644)")
(4-1) Charles I to Prince Maurice, 25 June 1644 (Parliamentary Archives)

(4-2) Letters from Charles I to Prince Rupert, March 1643 to April 1645 (Add MS 18983 (BL))
One from 29 April 1645 is not deciphered but can be read.

(5) "D: of Richemonds Cyfer"
Charles I to Prince Rupert, 31 July 1645 (Add MS 18983, ff.15-16).
This letter shows Charles changed his cipher used in correspondence with Rupert after Naseby. There is a note in the margin, "This is in the D: of Richemonds Cyfer." The Duke of Richmond had returned from exile to defend Oxford for the King (Wikipedia).
This is the same as what I previously reconstructed from Add MS 18982 f.79 (privately designated THE=g4). This cipher is interesting in providing for many nulls among low numbers, where typically single letters are assigned.
Specifically, while many of numbers 1-112 are for letters but most of 20-40 are nulls. When these nulls are well used (as in this letter), the codebreaker may have been led off track.
About the same time, Rupert used a different cipher with Nicholas ("Nicholas-Rupert Cipher after Naseby (July 1645)").
These specimens will help fill the gap in my reconstruction of the ciphers.

For the specific ciphers, see "King Charles I's Ciphers" (this article started with the few printed sources available at first, and need an overhaul with many archival materials now available online).