Because of the guaranteed attribution.imho, the first gives fulsome opportunities to Dremel Man, thus undermining any guarantee that the item is right.
Not sure about that, a signature can be documented, and specific components compared (as experts do with autographs). Although you have a point of course.
I realise you are being specific to Venini, but operating in a field such as mine, where everything is unsigned, there is little need for educated guesswork, as huge swathes are documented.
But you are generally looking material from major factories who, as you say, document their work thoroughly. I am talking here about studio glass makers, some very small, who may achieve fame and acclaim in the future. Their early works are VERY unlikely to be documented by them.
I guess the major difference between glass and ceramics is the material. A backstamp on ceramics is not normally visible from the front surface, whereas the transparency of glass may mean that the signature can actually impact on the viewer, directly. Perhaps the reason why much glass comes with removeable labels.
Also true, although some ceramics also have removeable labels.
I am just looking for the easy way out to gain more knowledge I suppose. I would like to KNOW for certain that something is by someone, so that then I can compare and learn about other aspects that make an item different to something similar.
My personal problem is that without the signature, the similarities can often outweigh the differences, making me very unsure of any attribution.