The vases are part of the "Intimates" range designed by Belinda Hornsey. I'm still not 100% sure about the date, but the design of the box I have would suggest mid to late 1990s.
If I have counted right, there are 8 designs, made up of four pairs at different heights. Each pair "interlock" i.e. where one vase bows outwards, the partner vase bows inwards.
There are four colours: Lavender, blue, green and clear crystal.
So there it is, no more confusion with Riihimaki!