It has been known from Karl de Leeuw's work that Dutch diplomatic ciphers provided multiple substitution tables.
Now, in deciphering a ciphertext in Thurloe State Papers, Paolo Rosson found it switches among five tables in one letter. Though the plaintext was found in a Dutch publication, the scheme he found out is interesting.
The ciphertext is something like "113. 10. 26. 13. 13. 19. 29. 29. 26. 11. 222. 31. 17. 21. 22. 23. 23. 22.13. 30. 20. 18. 22. 23. 15. 13. 24. 22. 13. 24. 22. 17. 10. 15. 25. 23. 13. 329. 28. 15. 22. 20. 25. 20. 15. 25. 27. 28. 20. 27. 27. 20. 22. 17. 20. 15. 527. 16. 20. 21. 12. 19. 21. 29. 26. 20. 16. 27. 16. 19...." Although the specimen is a bit short, I thought solving this would not be difficult.
As it turned out, this short letter switches tables multiple times. No wonder it couldn't be solved with ordinary attacks. (I said the plaintext might not be in Dutch but in French. Some may have been misled by this.)
The first digit of three-digit group indicates one of tables 1-5.
I uploaded a new article about this, "Table Switching in Dutch Diplomatic Ciphers".
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