this does beg the question Marcus - what makes you suggest Stuart - other factories such as Edinburgh, Webb Corbett, Thomas Webb, Waterford and possibly others, indulged in very similar cut patterns.
Of course, you may know that it came out of a Stuart presentation box.
The date alone does not mean there won't be a backstamp - most of the factories I've suggested did mark their wares at that period (and some still do) - although a small proportion of pieces always seem to escape the backstamp. It may well be any one of these makers, and simply have been one of the few that weren't marked.