Okay, here is an update on the 1700 Avery document.
I found the reference in the Archives of Scotland; you can ask for a copy of the original
She appears in the following background: "Papers of the Hamilton-Bruce family of Grange Hill and Falkland"
The copy was made on paper made in 1806, as indicated by the watermark embedded in it. So the copy is not earlier than 1806.
This document, as you can see, is not the original document but a copy. It is not 18th century. I stand corrected in my speculation. The document was in the Papers of the Hamilton-Bruce family of Grange Hill and Falkland
Source Country code : GB
Repository code : 234
Organization : NAS
Repository: National Records of Scotland
Reference : GD152/160
Copy memorandum on ‘Avery the Pirate’ and copy letter (27 Dec 1700) by him in cipher addressed to ‘Rev James Richardson at the library
over : against Orenge Street, St Martin’s-in-the-Fields, London’, with note : annexed of treasure-filled chests
Dates: [c1806]
Access status : Open
Level : Item
So, conclusion: the 1700 document, post-1806 document which states it's a copy of an earlier dated 1700 letter
addressed to ‘Rev James Richardson at the library over: against Orange Street, St Martin’s-in-the-Fields, London, It could be, but we cannot prove it beyond doubt.
So it is not indisputable evidence of what was said in 1700 because it's a copy of an alleged earlier correspondence over 100 years later.
So, to fully clarify, to prove or disprove the items of buried and alleged treasure attributed to Avery, we must find the original documents in the State Papers Online database.
February 22 Letter: Reference Code: SP 44/100/541 (State Papers Domestic, Entry Books, Volume 100, Page 541).
February 7 Letter: Reference Code: SP 44/100/541 (State Papers Domestic, Entry Books, Volume 100, Page 541).
May 27 letter: Reference code. Sp 44/101/163 (State Papers Domestic, Entry Books, Volume 101, Page 163).
Unfortunately, I am at sea. Riding out heavy weather, and it's not high up on my list of priorities
Crow