I am convinced that some of them are. I have handled 'The Dice is thrown' vase this week, by E.T. Siiroinen, and a Sun bottle, by Helena Tynell, both with stoppers and both of which I already have, without stoppers, so comparing was not too difficult. They were definitely from the same manufacturer. Colour, mould line, etc., were identical.
As for the Emma vase, I have only compared two of them, both different colours and the decanter not being clear cased. I have a blue one which is due to arrive, so I will compare it to the other blue Riihimaen glass that I have when it gets here.
I have the designlasin book, unfortunately, even though there is a rough translation guide at the back, it is not understandable to me in its entirety and there are also a lot of words which cannot be found at the back of the book either.
I will continue to try and find out more information and let you know if I find out anything else.