I can't see that they are the same shape to be honest. They look to have a small 'foot' and the shape of the 'bowl' of the vase looks slightly different, and where the neck on Selina's vase goes in quite obviously those ones appear to not have the same shape either.
I'm not so sure it has been cut down, but I could be wrong. It's a kind of 'gourd' shape in it's own way.
When you look at the rim under a magnifying glass is it bevelled on the inside and out? oops redundant question as I can see that it is. I suppose the only thing that would worry me is the trailing seeming to go right over the rim where is is cut. It looks a bit curious,but perhaps that would happen whereever it had been cut? I don't know anything about blowing glass and whether or not that might happen on these threaded pieces.
m