On page 31 of The Crystal Years under the Chapter 'Nineteenth Century Cameo' it says the following regarding marks:
'Unfortunately Stevens and Williams often failed to have all their wares artist signed and some were not even trade marked, ...
I find it very strange indeed that any author should consider an apparent failure or error a legitimate reason for any action or lack of action by such a successful business. It seems to me that when looking for a reason for anything to do with such businesses, a failure or error outcome simply indicates that you haven't considered enough possibilities.
It seems to me that S&W did not regard identifying themselves by marking objects important as regards Joe Public end user. Indeed marking would have caused stock control difficulties when a stock of unmarked pieces would have had to be maintained for trade buyers who did not want the maker identified — possibly Liberty's for example.
Just off the top of my head, possible reasons for an identifying mark might have included:-
Prominent "museum quality" pieces likely to end up displayed in important collections,Trade samples,Rep's samples,S&W's showroom pieces,Agent's showroom pieces,Exhibition pieces,Pieces "ordered by" or, more accurately, "donated to" Royalty*,Donated trophies, retirement gifts, and the like.Certainly limited use of the S&W mark along these lines would account for the mark's rarity. Is this suggestion realistic?
Bernard C.

* — Where did I see the piece about the most expensive objects being removed from exhibition stands when they knew that acquisitive Royalty was on its way?