Wow! That's some list, Gibb.

Just an observation or suggestion which I'm sure you consider already. Almost all of the earlier extracts are by English-speaking 'writers'/'observers using a well-used word in their own vocabulary with the 'church' sound, whereas the few French extracts would surely be using 'shush'. Is there any significant difference in the meaning of chaunt and chant, or are they synonymous?

Another aspect I haven't seen discussed is the use of the vowel sounds as in French 'shontay'. If the sailor/stevedore usage did derive in some way from the French would the earlier pronunciation have reflected this?