must admit Peter, I'd not thought of using wear in the comparative sense to assess age on stylistically related objects - as you say, there are too many variables for that method to be reliable. However, I am a fan of wear, and would rather see some than look at an alleged C18 or C19 piece and see almost nothing - but that's just a hang up I have - perhaps engendered by the copyist age we live - when there's so many fakes around.
I'm going to quote from Andy McConnell's book, and from the section on 'Moulded Decanters'.................
This author speaks at some length on Charles Chubsee and his revival of moulded wares made in two and three part moulds, at the very beginning of the C19 - an addition to the glass industry that apparently had more influence in the States perhaps than the U.K. (re bottles and decanters). Apparently he'd been engaged in some industrial espionage in Bohemia on behalf of his Stourbridge employers, and when back in Stourbridge ....
"Chubsee moulds were used to produce a variety of cheap table glass. Moulded square and barrel pint decanters with combinations of pillars, flutes and diamonds approximating costliercut finishes were made in Britain, Ireland and the United States until the 1850's."
This doesn't offer any proof that the decanter posted here is from Ireland, just that the Irish did use this method to make decanters, and equally many very similar moulded decanters were produced in the States.
Can we ask please what the pontil area looks like, and what evidence, if any, of moulded seams.
But coming back to the wear issue............this feature really mustn't be used as a 'key factor' in determining age, however tempting.
When assessing age there are many features that combine to offer a possible answer - and we mustn't jump to conclusions based on personal wishes.
quote................."I have many 16th and 17th century pieces that show very little ware at all , but that's because of there weight and metal , not there age."..............
Another possible reason for lack of wear in this instance is value.........we do tend to be a little more careful with expensive things as opposed to pressed tumblers and moulded decanters.
My glass ceases to accumulate wear from the day I buy it - no point in risking damage to expensive pieces.
sorry I don't have Dudley Westropp's book

- is it worth me getting please, it appears to be quite old?