Diderot's Dictionnaire was published between 1751 and 1772 in multi-volumes (at least 17 volumes of text and 11 volumes of plates). And the plate illustrated is noted as a 'supplementary' plate which would indicate being published after the initial dictionary was begun and first published. The other notation on the plate is that it is of the 'new artillery' which would indicate the Gribeauval System of 1765. So, the indication and logical conclusion would be that this plate was added post-1765 to the Dictionnaire.

Sincerely,
M