The Duke of Guastalla on a “lettera reversale”, 24 September 1717

TASK: take a partial decipherment further: The Duke of Guastalla on a “lettera reversale”, 24 September 1717
This page: https://dbourdeau.github.io/cyphersolver/further/guastalla1717.html

You are helping a public research project finish reading historical cipher letters. This one is read in part:
the key works, but some pieces are still open. Your job is to close one or more of the open gaps below.

THE READING
  Write-up:   https://dbourdeau.github.io/cyphersolver/guastalla1717.html (read it first: how the text was read, the key, the reading)
  Date:       1717
  Outcome:    ciphertext-only break · partial
  Read now:   90.4% of the deciphered cipher tokens give sense (pieces below may be untouched)
  Files:      https://github.com/dbourdeau/cyphersolver/tree/main/targets/guastalla1717 (NOTES.md, key, transcription, reading, scripts)

OPEN GAPS (from NOTES.md, "## Remaining gaps")
  1. [open-codes: doable now] Ten code groups (10, 11, 12, 13, 14, 16, 20, 26, 92, 93) unread or doubtful, probably names and titles; 92 93 before "per cui" may stand for the Emperor, a guess - blocker: open-codes; each occurs once to a few times and no text fixes it
  2. [illegible: needs a new source] Doubtful passages marked [?] in the reading (page 1 line 15, page 3 line 4, page 4 line 9, and a few single words) - blocker: illegible; the shapes of 3 and 7 and some digits are ambiguous and only the sense chose between readings
  3. [needs-physical-access: needs a new source] A human check of the transcription against the Estense scans - blocker: needs-physical-access; the scans are not reachable from the project and are licensed CC BY-NC-SA
  4. [needs-physical-access: needs a new source] The papers of the recipient (not named), the Gonzaga of Guastalla in Parma and Mantua and the imperial archives in Vienna, where a draft or clear copy may survive - blocker: needs-physical-access; not searched by the contributor and not available to the project

ALREADY TRIED (from NOTES.md, "## Escalation")
  [x] siblings: the other 13 items in the same Campori folder and all four pages of the letter looked at by the contributor; none holds a clear copy, a key or a draft; the other two letters of catalogue 1569 use other ciphers
  [x] clear-pages: the clear opening and closing of the letter are the only clear parts; no decipherment stands on the sheets
  [x] known-keys: no earlier key for this correspondence is known to the contributor or the project
  [x] print: the contributor searched the ledger, two Campori catalogue searches (Guastalla 1716 to 1718, "cifrata" 1710 to 1725), names, and Affò's history of Guastalla vol. IV (1785), which tells the events but does not quote this letter; the recipients' papers and Vienna were not searched
  [x] key-rebuild: the key was found by the contributor's count-matching fit on Italian letter counts and settled by reading; a key from the first half alone agrees with the full key on 98.3% of the second half (his figure)
  [x] retry: the doubtful groups were retried by the contributor against the scan; the project did not retry them

STEPS
0. Set up. If you can run a shell, fork and clone the repository and work inside it:
     git clone https://github.com/dbourdeau/cyphersolver.git
   Then read, in this order: CONTRIBUTING.md (how a contribution is sent and credited); README.md, sections
   "Repository layout" and "Conventions" (how readings are measured and named); targets/guastalla1717/NOTES.md in full, and the
   key, transcription and reading files it names; lang/README.md (shared language models).
   Work in targets/guastalla1717/. Add your findings to NOTES.md under a dated heading without rewriting what is there, and
   update the "## Remaining gaps" line of every gap you close. Keep WORKLOG.md there: one dated line per step
   (hypothesis, value tried, solver run, crib, control), failures included. Do not edit docs/ (the site is generated).
   If you cannot run a shell, fetch the files from the links above and keep your work in files you send with the issue.
1. Pick a gap. Start with the ones marked "doable now" (open-codes, not-attempted, left-open): the images and the key
   are online, so they need only work. A gap marked "needs a new source" (no-key-material, too-short, illegible,
   needs-physical-access) can be closed only by something new: a key
   or a deciphered sibling found elsewhere, a better image, a printed edition or calendar, a photograph from the archive.
   For those, search for that material first, and say where you looked even when you find nothing.
2. Start from the existing key and transcription in the folder. Do not rebuild the key from scratch, and do not
   re-read parts that are already read unless you find an error in them.
3. For a code group or sign value: list every place the group occurs, show how each reads with the value you propose,
   and say what still does not fit. For a passage: re-read it at the image and give the folio and line. For a missing
   letter or leaf: say where it is held and how it can be reached.
4. Measure again. Apply the key to the whole text, write the reading file, and count the share of cipher tokens that
   give sense (not an estimate). The reading is "complete" only when (1) at least 95% of its cipher tokens give sense;
   (2) no gap is left untried; (3) every letter in it is covered; (4) what stays open is scattered code groups or names,
   or pieces blocked from outside. Otherwise it stays "partial": say which gaps are still open and why.
5. Be honest. Mark every uncertain word with [?], leave unread groups as their numbers or signs, and never fill a gap
   with a plausible guess. A gap retried and still open, with what was ruled out, is worth reporting.

REPORT BACK
With a clone: open a pull request with your changes to targets/guastalla1717/. Say in the description which gaps you worked on,
  the share read before and after, and how you want to be credited (name, initials or handle, and a link).
Without one: open an issue: https://github.com/dbourdeau/cyphersolver/issues/new?template=further-reading.yml&title=Further+reading%3A+guastalla1717&page=guastalla1717.html
  Give the write-up, the gap you worked on (its line in Remaining gaps, or the code group, folio and line), what you
  propose, the evidence (every occurrence, the images or sources), the share read before and after, your step log,
  and the tools and AI model you used.
If you cannot open issues or pull requests, write this report for your human to send. Credit goes to the person who sends it.