"Duplicate copies have at once been dispatched, "

Apparently Prof. Xie did not have appropriate understanding of "duplicate copies". If Dr. Fang in his article adds an accurate translation of this wording, it may help show the point even clearer to people like Prof. Xie.

All published books are "copies". "Duplicate" means duplicating what the club mailed the first time; second copies were identical to the first copies. Even put in correspondences nowadays the wording in the context wouldn't involve a copier machine.