Lady Liberty
Your comments that the Society's use of Grayson's publication by altering ir inserting their dates is somehow dishonest or improper shows that you have know knowledge of academic practice or convention. The Society has done nothing wrong by inserting a different date enclosed within square brackets because this is done to indicate to the reader that a correction or explanation is made. You should consult a Style Manual to verify this and if you are living in the USA then the most popular Style Manual is the Chicago Manual of Style, for authors, editors and copyrighters. The Society as a longtime publicher has also its Syle Manual adopted for its own use which also is the case with most Government department, Institutions such as Universities.
So, as long as the adjusted date is enclosed within square brackets and within the quotation followed bythe source properly referenced then everything is OK.
scholar JW