Hard to tell if it's deep enough to remove 3/4 of a gram. If it was much less in weight I'd worry but I don't think it's worth worrying about unduly.
Unless it is thicker or larger in any dimension than the other bars?
I'd just measure it and do the s.g. test to remove any niggling doubt if it's going to nag at you.
Could they have flattened/polished the rear before engraving it which might have removed a little more silver?
I think I preferred the last shillings we used to use as 5p to these. The English 3 lions and Scottish lion Royal arms ones.
Not that the putting all the coins together to make one coat of arms was that bad an idea either.