Hello,
There were some 400 pieces in the Count Lionel de Minerbi Service made by James Powell & Sons in 1906, which was based on a piece shown at the Turin Exhibition of 1902. This piece was bought from the exhibition by Minerbi, who then commissioned his own service based upon (it is believed) the threading used by Powell in this item. (It is not known what the actual item was that Minerbi bought).
NB. Various sources suggest, under 400 pieces, 400 pieces (both Jackson, ed) and 465 pieces (Hajdamach, 2009) in the Minerbi suite.
Another service, having different coloured threading, is also known meaning that it is also possible to determine which service an item eminates from.
Bernard, it is nice to know that you have so much confidence in your fellow dealers that you advise Bonhams above Jeanette Hayhurst, The Country Seat or even myself - all of whom have a depth of knowledge in the subject of early Powell that people such as Simon Cottle (and other auction houses) turn to us for advice.
Should you need advice on your pieces Marcel I would be happy to help you, please email me nbenson at 20thcentury-glass dot com assuming Hobbsy hasn't already put you right.
Nigel