A letter in code with interlined deciphering by the Cardinal of Rohan (Wikipedia) is presented in transcription by Daniel Tant (pdf). The letter, dated Rome, 21 July 1721, is found in the municipal archives of Reims, carton XVI, nos.49, 50.
The highest number used is 841. The figures 10-55 are assigned to the letters of the alphabet (two for each letter) in a regular order. The figures 100-589 represent words and syllables. The figures "800 (le) pape" and above are for names.
The arrangement in the nomenclature section (100-589) is not random. When one examines the code, it will be noted that syllables beginning with the same consonant are given figures with intervals of 10: ha (324), hi (344), ho (354), hu (364), etc. The original cipher would have had a table with code numbers increasing horizontally and word elements arranged vertically. Such a scheme is also found in codes during the age of Louis XIV (see another article, items (3)(4)(8B)).