We're pretty sure (as I said) that this is a false lead...but it's not impossible.
The Viane lampshades are in a completely different style, and the marks imply that the ARTA name is the retailer or lamp maker, not the factory.
If it WERE a (Belgian) factory then it would be odd that the Viane items bear no resemblance at all to anything else produced in Belgium nor to either of the labelled examples. The two labelled examples in my previous post (above), in contrast are quite typical of Belgian (pre-war) production and have several characteristics to support that, besides the style of the label.
The name Arta is likely to be a range rather than a name of a place/factory. There is no reference to it in Massart's comprehensive book, nor is the name recorded by the government as an employer.
Other examples of labelled ranges with unidentified producers are on my website (Chanteclair, Mimosa, Belle Garde, etc)
http://www.hogelandshoeve.be/index075.htmlHaving said which I cannot absolutely disprove either of the other theories, but will point out that yes, labels were stuck on the middle of plates and bowls, and typically on the waist or neck of (baluster) vases, so I see no reason to think it indicates the label belongs to a third party.