Hi - sorry to hear of the problems.
Firstly to say I've no knowledge as to whether this Stuart pattern, or any others for that matter have been copied in recent times - I simply don't collect these modern drinking glasses.
We've had a similar situation in recent times - discussed on the GMB - involving a named pattern from Edinburgh Crystal, where that buyer was equally adamant that the items they received from the seller, whilst described as the same pattern, were sufficiently different in appearance to make the buyer believe the glasses were not the design they ordered.
In that instance - and possibly with this case too - the problem was caused by the glasses in question being manufactured in another country.
Edinburgh Crystal became Edinburgh International, and their work was outsourced to Czechoslovakia, and the appearance of the pattern in question seems to have changed more than expected - not a problem until you want to make up a set should some have been broken etc.
Do you have the original packaging Pete - do you know where your glasses were made?
How do your glasses compare with the Replacements.com site for this Stuart pattern, which presumably is called Fuschia. Did Stuart produce more than one pattern with fuschia wheel engraving etc.? Believe this backstamp is the most recent one, so certainly not old glasses.
There probably was a time when the appearance of named designs changed very little, and dimensions of the glasses remained constant, but in this throw away age, standards simply aren't what they used to be, and perhaps even the introduction of additional mechanical process, has had the effect of altering appearances.
Assume all of the pix we see are of your glasses, and none shows the buyers pieces, so we unable to make comparisons. You'll understand that it's probably not appropriate for us to act as arbitrators in these situations - however, you've done the correct thing and refunded the buyer, and would suggest you don't berate yourself - from what you've said it appears there was no intentions to deceive. Regret my reply lacks any positive answer for you, and this may remain an unresolved issue.
Hindsight is easy, but it might be worthwhile in future similar situations to send buyers images of exactly what it is that you're going to send them - but think most folk here would agree there's not been any attempt to deceive.
Let's see if others can contribute something more positive and useful.