also I think from reading the reports,that it seems unlikely there would have been much American glass over here in the UK in that late 19th century period.
The report seems to ask how they can increase their exports to the various countries and the answer seems to be ... produce the products people want in that country, produce them on time, ship them on time and with packing rates that are comparable to competitors in Europe and have sales people over in the countries to sell the items.
The few I've read don't seem to indicate there are any insurmountable trade barriers in comparison to other countries so trade agreements/import tax doesn't seem to be the problem. It does appear that they were trying to find a way of increasing their trade with European countries.
Therefore, along with the design indicators, I'd say the opaline vases in this thread are more likely to be French than American?