Undeciphered Superscription by Edward Hyde in Brussels (1659-1660)

When I was browsing the Latin edition of Life of John Barwick, I noticed some letters by Edward Hyde in Brussels just before the Restoration have superscription in cipher (probably concealing the recipient(s)). The superscription is omitted in the English version. (The Latin version leaves letters in the appendix in English.) I added a section "Undeciphered Superscription by Hyde (1659-1660)" about this in "King Charles II's Ciphers during Exile". I also mentioned it in "Unsolved Historical Ciphers".