I’m not sure that faceting diagrams that haven’t been formally published in a book or magazine fall into protection at all. I doubt it, as there is no way to prove the date of authorship.
Not true. Copyright exists from the moment a work is put in tangible form. If you think a work is past copyright and are challenged, it’s up to you to prove the age, not the copyright holder.
it’s essential that I am able to have unrestricted access to prior written works.
Are you confusing distribution and access? Nothing prevents you from having access to any work you can find, and even publishing bits of it under the fair use rules.
I think we should definitely have open access to all the old diagramS of Faceters who are long dead. Why not?
The authors may be dead, but their estates still exist. Do you think your home should become public domain after you die?