Hi Fred - thanks for the additional information.
Unless qualified in some other way, then it's probably true for most if not all of Europe, that when we use the word 'threaded', we are referring specifically to the practice of decorating the item with a continuous fine thread of actual glass, whether clear or coloured. Aside from historic examples, the sort of threading we're speaking of here was applied manually in the C19, until c. 1875 - so two guys, with one to revolve the item and the other to feed the plastic glass threading in an evenly spaced appearance. After this date I think it was applied mechanically - but the real thing should be apparent as a single thread, and it will be distinctly proud of the body - sometimes it falls off where adhesion was poor or contact with something has broken the thread away. The accuracy of application and the uniformity of the thread was usually very good - there shouldn't be any significant waviness in the line of thread, and even when coloured, there shouldn't be any doubt as to the fact it's glass.
Enamel as an applied form of decoration has a long history, and almost certainly would not have the same round cross section appearance as glass, if it were used to simulate a thread - visually it would be opaque and have a much flatter appearance.
By its nature, threading is applied to a revolving object, and unless there was some form of masking-off where the leaves appear, then it would be very untypical to see areas without threading, assuming it had been created by traditional methods using glass thread. Your leaves appear to have been created using the same material as the white banding -which looked to my eyes as though there was a possibility both the white and green were enamels - but this is only supposition on my part - I could well be very wrong.
the shape of your vase is very unusual - the silence so far doesn't bode well for an attribution, at least from us European guys. Have you shown this to your States friends? Regret the marking means nothing to me.

P.S. sorry, the point about trying to discern whether glass threading or enamel painted decoration is ................ The Victorians were big in glass threading, so depending on which sort you have will be a general indication as to whether C19 or C20.