Congratulations, Dave! A lovely 'find' :hiclp:
Now for your logic ...

Personally, I would agree firstly that your new Amethyst tazza was probably made by the same company as your vaseline one.
Recently (and here I should apologise to KevH, as I was going to write a post about this but never got round to it

) Kevin and I compared several pieces of uranium glass from my collection, and also some of his, under UV - both long and short wave. We found that, for the most part, the UV 'matches' confirmed the ordinary light matches. However, we did find that one particular piece of his matched
exactly one of my uranium 'rustic' pieces in every respect - except that his was made in part uranium and part non-uranium glass!
However, looking at the leafy feet of your tazza, I can see both similarities and differences to the Walsh brocade piece in Mike Weedon's picture. And I have many examples in my collection with leafy feet which look superficially the same, but have small differences in construction - for example, tooling marks. Personally, I would not like to make a match from a photo alone.
Likewise the twist in the stem. I have a couple of items which have a similar twist in the stem, but I wouldn't assume they were made by the same company as your tazzas.
As for Cyril Manley, I am not going to get into a 'debate'

about the accuracy or otherwise of his attributions, as I have had my wrist slapped before on this subject

However, I would simply say that some people think his attributions are wildly inaccurate, being based largely on anecdotal evidence (and indeed many have been found to be wrong, following subsequent research) while others trust his knowledge - strangely, for the same reasons! He lived in the Stourbridge area and based many of his attributions on personal conversations with ex glass-workers from that area.
I'm really looking forward to hearing what Bernard and Christine, amongst our other experts on this sort of glass, have to say about this!