Many thanks Ohio
a couple of points which I think are right (but folk please chip in if you disagree) -mostly for clarity of other readers;
The USA required country of origin marked on foreign made items from, oh gosh, I think 1890 (McKinley Tariff act -or the 1893 amendment) -as they had to put the country of origin on all their wares sold into USA - Loetz added the company name too -mostly marking Loetz Austria (technically not the country of origin, but close enough -depends how you define country) variants of the McKinley act still stand I believe.
At its peak Loetz got quite big (if Alisa is around she's better on this) they had 3 glass producing sites -in an around immediate area. Not sure of employee numbers.
Also like many bohemian glass makers Loetz did not really 'make and then sell' they pretty much only made what had been commissioned by retailers -so it wasn't Loetz selling in the USA - it was US retailers commissioning work from Loetz and importing it -these retailers were quite likely to be importing from Kralik, Rindskopf etc etc too (hence much of the confusion)
Many books claim Loetz directly copied Tiffany's style - but I've always found this very unlikely -biggish influence maybe -but the whole idea of making this kind of iridised glass came from much closer to home. Way way before either made Iridised glass - it was first commercially made, much earlier (1873) and only 10 miles down the road from Loetz by Wilheim Kralik - when he ran Meyr's Neffe glass and it was made exclusively for Lobmeyr (oh and following a formula nicked from the Hungarian Leo Valentin Pantocsek).
sorry enough of my wittering!
M