judging by information in the 'big book', the initial agreement with Elfverson's & Co. in '31 was cancelled almost as soon as it was signed, and a further contract signed with Wuidart within a matter of months with advertising material showing Wuidart's name. I could be wrong, but previously I'd imagined there may not have actually been any business done with Elfverson whereby they were supplied with any glass, but ............... quoting from the big book it comments ............. "Pieces made for Elfverson's are very heavy, sometimes weighing around 8kg (18 lbs) with large optic effects and rather Nordic colours ................. etc."
The implication of this comment might suggest that Efverson's took an initial delivery, though that's speculation on my part. No idea if anyone has ever found an Elfverson's label.
Otherwise it appears we only know of Wuidart as the sole agent for the 'Wealdstone' range.