Early French Figure Ciphers

An early specimen of a French figure cipher (digit cipher, numerical cipher) is discussed in Camille Desenclos and George Lasry, "An early French digit cipher: deciphering a letter from the King of France to the Duke of Nevers (1592)" (HistoCrypt 2024).
It is used in a letter from Henry IV to Duke of Nevers, 12 September 1592 (BnF fr.3620, f.70-71)(p.47). The cipher employs variable-length figures written continuously, but the authors could parse the ciphertext into cipher symbols by assuming three-digit figures always start with "1" (p.48; see also my articles from 2017-2019 and 2018-2019). After the key was reconstructed, the authors found the original cipher table among Nevers' collection of keys in BnF fr.3995, fol.140 (p.49).
Many cipher letters between Henry IV and the Duke of Nevers have been known but they used conventional symbol ciphers in BnF fr.3995, fol.67 rather than numerical ciphers (p.49-50, 46; see also my article). The authors point out that the 1592 letter in question is countersigned by Martin Ruzé de Beaulieu, while all the other letters in cipher from the king to the duke from 1591 to 1594 are counstersigned by Louis Potier de Gesvres (p.49-50). The 1592-cipher was also used in letters in 1591 to Henry IV (two from Duke of Biron, one from sieur de Guitry, baron de Salagnac, and marquis de Pisani) (p.51).
The papers is also valuable in citing many examples of exclusively digit ciphers in the 1580s/1590s (p.50; see also other figure ciphers mentioned in my articles: Henry III etc., Buzenval).

(5 July 2024) I now remembered another French ciphertext in variable-length figures (1, 2, or 3 digits) written continuously (ca.1620?) is discussed in here.

(24-25 August 2024) The paper points out at least 23 letters sent to the Duke of Nevers in 1589-1591 use only digits (p.50). To this list may be added another ciphertext in digits continuously written without break (since it is not deciphered, we cannot tell whether it employs variable-length symbols). The ciphertext is in an Italian letter from Lodovico Birago to the Duke of Nevers, 13 November 1571 (BnF fr.3251, f.119), which I mentioned here some years ago.