Peter Grund (Yale University), Erik Smitterberg (Uppsala University) and Matti Peikola (University of Turku) are co-writing a paper about recorders’ use of the ampersand (vs. and) in the Salem witch trial documents of the 1690s.
One of the questions they are pondering has to do with possible contemporary prescriptivist notions concerning the use of the ampersand, for example in writing manuals, grammars or spelling books. They would be grateful to know if anyone has come across any comments of this kind, for example instructing writers to avoid (or prefer) the ampersand – or even abbreviations more generally – in some kinds of texts or contexts?
Any tips for potentially useful primary or secondary sources would be greatly appreciated (address for correspondence: matti.peikola[at]utu.fi). But comments may be posted here as well.
Bridging the Unbridgeable 
Well, letter-writing manuals did not encourage abbreviations in Late Modern times, and yet in family correspondence use of <+> instead of <and> is normal. Besides, trial proceedings are a text type of their own. What is observed in https://www.oldbaileyonline.org/?
The American Screenwriter’s Guild has very specific prescriptions for the use of ‘and’ and ampersands when it comes to writing credits in television scripts; doesn’t pertain to general usage but interesting.